diff --git a/samples/demo-app/app/src/main/java/cash/z/wallet/sdk/demoapp/demos/send/SendFragment.kt b/samples/demo-app/app/src/main/java/cash/z/wallet/sdk/demoapp/demos/send/SendFragment.kt
index 95cf112a..e694232c 100644
--- a/samples/demo-app/app/src/main/java/cash/z/wallet/sdk/demoapp/demos/send/SendFragment.kt
+++ b/samples/demo-app/app/src/main/java/cash/z/wallet/sdk/demoapp/demos/send/SendFragment.kt
@@ -2,19 +2,18 @@ package cash.z.wallet.sdk.demoapp.demos.send
 
 import android.view.LayoutInflater
 import android.view.View
-import android.widget.Toast
+import android.widget.TextView
 import androidx.lifecycle.lifecycleScope
 import cash.z.wallet.sdk.Initializer
 import cash.z.wallet.sdk.Synchronizer
 import cash.z.wallet.sdk.block.CompactBlockProcessor
 import cash.z.wallet.sdk.demoapp.App
 import cash.z.wallet.sdk.demoapp.BaseDemoFragment
+import cash.z.wallet.sdk.demoapp.R
 import cash.z.wallet.sdk.demoapp.databinding.FragmentSendBinding
 import cash.z.wallet.sdk.demoapp.util.SampleStorageBridge
 import cash.z.wallet.sdk.entity.*
 import cash.z.wallet.sdk.ext.*
-import kotlinx.coroutines.flow.collect
-import kotlinx.coroutines.launch
 
 class SendFragment : BaseDemoFragment<FragmentSendBinding>() {
     private val config = App.instance.defaultConfig
@@ -23,6 +22,36 @@ class SendFragment : BaseDemoFragment<FragmentSendBinding>() {
     private lateinit var synchronizer: Synchronizer
     private lateinit var keyManager: SampleStorageBridge
 
+    private lateinit var amountInput: TextView
+    private lateinit var addressInput: TextView
+
+
+    //
+    // Observable properties (done without livedata or flows for simplicity)
+    //
+
+    private var availableBalance = -1L
+        set(value) {
+            field = value
+            onUpdateSendButton()
+        }
+    private var isSending = false
+        set(value) {
+            field = value
+            if (value) Twig.sprout("Sending") else Twig.clip("Sending")
+            onUpdateSendButton()
+        }
+    private var isSyncing = true
+        set(value) {
+            field = value
+            onUpdateSendButton()
+        }
+
+
+    //
+    // BaseDemoFragment overrides
+    //
+
     override fun inflateBinding(layoutInflater: LayoutInflater): FragmentSendBinding =
         FragmentSendBinding.inflate(layoutInflater)
 
@@ -32,13 +61,30 @@ class SendFragment : BaseDemoFragment<FragmentSendBinding>() {
         synchronizer = Synchronizer(App.instance, config.host, initializer.rustBackend)
     }
 
+    // STARTING POINT
     override fun onResetComplete() {
-        initSendUI()
+        initSendUi()
         startSynchronizer()
-        monitorStatus()
+        monitorChanges()
     }
 
-    private fun initSendUI() {
+    override fun onClear() {
+        synchronizer.stop()
+        initializer.clear()
+    }
+
+
+    //
+    // Private functions
+    //
+
+    private fun initSendUi() {
+        amountInput = binding.root.findViewById<TextView>(R.id.input_amount).apply {
+            text = config.sendAmount.toString()
+        }
+        addressInput = binding.root.findViewById<TextView>(R.id.input_address).apply {
+            text = config.toAddress
+        }
         binding.buttonSend.setOnClickListener(::onSend)
     }
 
@@ -48,7 +94,7 @@ class SendFragment : BaseDemoFragment<FragmentSendBinding>() {
         }
     }
 
-    private fun monitorStatus() {
+    private fun monitorChanges() {
         synchronizer.status.collectWith(lifecycleScope, ::onStatus)
         synchronizer.progress.collectWith(lifecycleScope, ::onProgress)
         synchronizer.balances.collectWith(lifecycleScope, ::onBalance)
@@ -56,11 +102,12 @@ class SendFragment : BaseDemoFragment<FragmentSendBinding>() {
 
     private fun onStatus(status: Synchronizer.Status) {
         binding.textStatus.text = "Status: $status"
-    }
-
-    override fun onClear() {
-        synchronizer.stop()
-        initializer.clear()
+        if (status == Synchronizer.Status.SYNCING) {
+            isSyncing = true
+            binding.textBalance.text = "Calculating balance..."
+        } else {
+            isSyncing = false
+        }
     }
 
     private fun onProgress(i: Int) {
@@ -69,39 +116,69 @@ class SendFragment : BaseDemoFragment<FragmentSendBinding>() {
             else -> "Downloading blocks...$i%"
         }
         binding.textStatus.text = message
+        binding.textBalance.text = ""
     }
 
     private fun onBalance(balance: CompactBlockProcessor.WalletBalance) {
-        binding.textBalances.text = """
+        availableBalance = balance.available
+        binding.textBalance.text = """
             Available balance: ${balance.available.convertZatoshiToZecString()}
             Total balance: ${balance.total.convertZatoshiToZecString()}
         """.trimIndent()
-        binding.buttonSend.isEnabled = balance.available > 0
-        binding.textStatus.text = "Synced!"
     }
 
     private fun onSend(unused: View) {
-        // TODO: add input fields to the UI. Possibly, including a scanner for the address input
+        isSending = true
+        val amount = amountInput.text.toString().toDouble().convertZecToZatoshi()
+        val toAddress = addressInput.text.toString()
         synchronizer.sendToAddress(
             keyManager.key,
-            0.0024.toZec().convertZecToZatoshi(),
-            config.toAddress,
+            amount,
+            toAddress,
             "Demo App Funds"
         ).collectWith(lifecycleScope, ::onPendingTxUpdated)
     }
 
     private fun onPendingTxUpdated(pendingTransaction: PendingTransaction?) {
+        val id = pendingTransaction?.id ?: -1
         val message = when {
             pendingTransaction == null -> "Transaction not found"
-            pendingTransaction.isMined() -> "Transaction Mined!"
-            pendingTransaction.isSubmitted() -> "Successfully submitted transaction!"
-            pendingTransaction.isFailedEncoding() -> "ERROR: failed to encode transaction!"
-            pendingTransaction.isFailedSubmit() -> "ERROR: failed to submit transaction!"
-            pendingTransaction.isCreated() -> "Transaction creation complete!"
-            pendingTransaction.isCreating() -> "Creating transaction!"
+            pendingTransaction.isMined() -> "Transaction Mined (id: $id)!\n\nSEND COMPLETE".also { isSending = false }
+            pendingTransaction.isSubmitSuccess() -> "Successfully submitted transaction!\nAwaiting confirmation..."
+            pendingTransaction.isFailedEncoding() -> "ERROR: failed to encode transaction! (id: $id)".also { isSending = false }
+            pendingTransaction.isFailedSubmit() -> "ERROR: failed to submit transaction! (id: $id)".also { isSending = false }
+            pendingTransaction.isCreated() -> "Transaction creation complete! (id: $id)"
+            pendingTransaction.isCreating() -> "Creating transaction!".also { onResetInfo() }
             else -> "Transaction updated!".also { twig("Unhandled TX state: $pendingTransaction") }
         }
-        twig("PENDING TX: $message")
-        Toast.makeText(App.instance, message, Toast.LENGTH_SHORT).show()
+        twig("Pending TX Updated: $message")
+        binding.textInfo.apply {
+            text = "$text\n$message"
+        }
     }
+
+    private fun onUpdateSendButton() {
+        with(binding.buttonSend) {
+            when {
+                isSending -> {
+                    text = "➡ sending"
+                    isEnabled = false
+                }
+                isSyncing -> {
+                    text = "⌛ syncing"
+                    isEnabled = false
+                }
+                availableBalance <= 0 -> isEnabled = false
+                else -> {
+                    text = "send"
+                    isEnabled = true
+                }
+            }
+        }
+    }
+
+    private fun onResetInfo() {
+        binding.textInfo.text = "Active Transaction:"
+    }
+
 }
diff --git a/samples/demo-app/app/src/main/res/layout/fragment_send.xml b/samples/demo-app/app/src/main/res/layout/fragment_send.xml
index 56470973..91942426 100644
--- a/samples/demo-app/app/src/main/res/layout/fragment_send.xml
+++ b/samples/demo-app/app/src/main/res/layout/fragment_send.xml
@@ -2,7 +2,6 @@
 <androidx.constraintlayout.widget.ConstraintLayout
     xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto"
-    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent">
 
@@ -15,14 +14,32 @@
         app:layout_constraintHorizontal_chainStyle="packed"
         app:layout_constraintStart_toStartOf="parent"
         app:layout_constraintTop_toTopOf="parent"
-        app:layout_constraintVertical_bias="0.2">
+        app:layout_constraintVertical_bias="0.05">
 
         <com.google.android.material.textfield.TextInputEditText
-            android:id="@+id/text_block_height"
+            android:id="@+id/input_amount"
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:ems="8"
-            android:hint="amount"
+            android:hint="zec amount"
+            android:inputType="number"
+            android:textSize="20sp" />
+    </com.google.android.material.textfield.TextInputLayout>
+
+    <com.google.android.material.textfield.TextInputLayout
+        android:id="@+id/text_layout_address"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        app:layout_constraintHorizontal_chainStyle="packed"
+        app:layout_constraintStart_toStartOf="@id/text_layout_amount"
+        app:layout_constraintTop_toBottomOf="@id/text_layout_amount">
+
+        <com.google.android.material.textfield.TextInputEditText
+            android:id="@+id/input_address"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:ems="8"
+            android:hint="to address"
             android:inputType="number"
             android:textSize="20sp" />
     </com.google.android.material.textfield.TextInputLayout>
@@ -46,14 +63,30 @@
         android:layout_marginTop="32dp"
         android:text="Initializing wallet..."
         app:layout_constraintStart_toStartOf="@id/text_layout_amount"
-        app:layout_constraintTop_toBottomOf="@id/text_layout_amount" />
+        app:layout_constraintTop_toBottomOf="@id/text_layout_address" />
 
     <TextView
-        android:id="@+id/text_balances"
+        android:id="@+id/text_balance"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_marginTop="16dp"
         app:layout_constraintStart_toStartOf="@id/text_status"
-        app:layout_constraintTop_toBottomOf="@id/text_status"
-        android:text="Available balance: --\nTotal balance: --" />
+        app:layout_constraintTop_toBottomOf="@id/text_status" />
+
+    <ScrollView
+        android:layout_width="0dp"
+        android:layout_height="0dp"
+        app:layout_constraintStart_toStartOf="@id/text_balance"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintTop_toBottomOf="@id/text_balance"
+        app:layout_constraintBottom_toBottomOf="parent"
+        >
+        <TextView
+            android:id="@+id/text_info"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="8dp"
+            android:paddingEnd="8dp"
+            android:paddingBottom="48dp"/>
+    </ScrollView>
 </androidx.constraintlayout.widget.ConstraintLayout>
\ No newline at end of file
diff --git a/src/main/java/cash/z/wallet/sdk/SdkSynchronizer.kt b/src/main/java/cash/z/wallet/sdk/SdkSynchronizer.kt
index bf497251..b0db06ce 100644
--- a/src/main/java/cash/z/wallet/sdk/SdkSynchronizer.kt
+++ b/src/main/java/cash/z/wallet/sdk/SdkSynchronizer.kt
@@ -1,7 +1,6 @@
 package cash.z.wallet.sdk
 
 import android.content.Context
-import androidx.paging.PagedList
 import cash.z.wallet.sdk.Synchronizer.Status.*
 import cash.z.wallet.sdk.block.CompactBlockDbStore
 import cash.z.wallet.sdk.block.CompactBlockDownloader
@@ -254,16 +253,19 @@ class SdkSynchronizer internal constructor(
         // TODO: this would be the place to clear out any stale pending transactions. Remove filter
         //  logic and then delete any pending transaction with sufficient confirmations (all in one
         //  db transaction).
-        manager.getAll().first().filter { !it.isMined() }.forEach { pendingTx ->
-            twig("checking for updates on pendingTx id: ${pendingTx.id}")
-            pendingTx.rawTransactionId?.let { rawId ->
-                ledger.findMinedHeight(rawId)?.let { minedHeight ->
-                    twig("found matching transaction for pending transaction with id" +
-                            " ${pendingTx.id} mined at height ${minedHeight}!")
-                    manager.applyMinedHeight(pendingTx, minedHeight)
+        manager.getAll().first().filter { it.isSubmitSuccess() && !it.isMined() }
+            .forEach { pendingTx ->
+                twig("checking for updates on pendingTx id: ${pendingTx.id}")
+                pendingTx.rawTransactionId?.let { rawId ->
+                    ledger.findMinedHeight(rawId)?.let { minedHeight ->
+                        twig(
+                            "found matching transaction for pending transaction with id" +
+                                    " ${pendingTx.id} mined at height ${minedHeight}!"
+                        )
+                        manager.applyMinedHeight(pendingTx, minedHeight)
+                    }
                 }
             }
-        }
     }
 
 
@@ -287,13 +289,15 @@ class SdkSynchronizer internal constructor(
         manager.initSpend(zatoshi, toAddress, memo, fromAccountIndex).let { placeHolderTx ->
             emit(placeHolderTx)
             manager.encode(spendingKey, placeHolderTx).let { encodedTx ->
-                manager.submit(encodedTx)
+                if (!encodedTx.isFailedEncoding() && !encodedTx.isCancelled()) {
+                    manager.submit(encodedTx)
+                }
             }
         }
     }.flatMapLatest {
-        twig("Monitoring pending transaction for updates...")
+        twig("Monitoring pending transaction (id: ${it.id}) for updates...")
         manager.monitorById(it.id)
-    }
+    }.distinctUntilChanged()
 }
 
 
diff --git a/src/main/java/cash/z/wallet/sdk/ext/CurrencyFormatter.kt b/src/main/java/cash/z/wallet/sdk/ext/CurrencyFormatter.kt
index 69b9bf12..eb219461 100644
--- a/src/main/java/cash/z/wallet/sdk/ext/CurrencyFormatter.kt
+++ b/src/main/java/cash/z/wallet/sdk/ext/CurrencyFormatter.kt
@@ -141,6 +141,15 @@ inline fun Double?.toZec(decimals: Int = ZEC_FORMATTER.maximumFractionDigits): B
     return BigDecimal(this?.toString() ?: "0.0", MathContext.DECIMAL128).setScale(decimals, ZEC_FORMATTER.roundingMode)
 }
 
+/**
+ * Format a Double Zec value as a Long Zatoshi value, by first converting to Zec with the given
+ * precision.
+ * Start with Zec -> End with Zatoshi.
+ */
+inline fun Double?.convertZecToZatoshi(decimals: Int = ZEC_FORMATTER.maximumFractionDigits): Long {
+    return this.toZec(decimals).convertZecToZatoshi()
+}
+
 /**
  * Format a BigDecimal Zec value as a BigDecimal Zec value, right-padded to the given number of fraction digits.
  * Start with Zec -> End with Zec.
diff --git a/src/main/java/cash/z/wallet/sdk/transaction/PersistentTransactionManager.kt b/src/main/java/cash/z/wallet/sdk/transaction/PersistentTransactionManager.kt
index 192b9181..e59b2334 100644
--- a/src/main/java/cash/z/wallet/sdk/transaction/PersistentTransactionManager.kt
+++ b/src/main/java/cash/z/wallet/sdk/transaction/PersistentTransactionManager.kt
@@ -1,8 +1,6 @@
 package cash.z.wallet.sdk.transaction
 
 import android.content.Context
-import androidx.lifecycle.LifecycleOwner
-import androidx.lifecycle.Observer
 import androidx.room.Room
 import androidx.room.RoomDatabase
 import cash.z.wallet.sdk.db.PendingTransactionDao
@@ -15,6 +13,7 @@ import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.coroutines.withContext
+import java.lang.IllegalStateException
 import kotlin.math.max
 
 /**
@@ -134,14 +133,14 @@ class PersistentTransactionManager(
     }
 
     override suspend fun submit(pendingTx: PendingTransaction): PendingTransaction = withContext(Dispatchers.IO) {
-        var tx1 = pendingTransactionDao { findById(pendingTx.id) }
-        if(tx1 == null) twig("unable to find transaction for id: ${pendingTx.id}")
-        var tx = tx1!!
+        // reload the tx to check for cancellation
+        var storedTx = pendingTransactionDao { findById(pendingTx.id) } ?: throw IllegalStateException("Error while submitting transaction. No pending transaction found that matches the one being submitted. Verify that the transaction still exists among the set of pending transactions.")
+        var tx = storedTx
         try {
             // do nothing when cancelled
             if (!tx.isCancelled()) {
                 twig("submitting transaction to lightwalletd - memo: ${tx.memo} amount: ${tx.value}")
-                val response = service.submitTransaction(tx.raw!!)
+                val response = service.submitTransaction(tx.raw)
                 val error = response.errorCode < 0
                 twig("${if (error) "FAILURE! " else "SUCCESS!"} submit transaction completed with response: ${response.errorCode}: ${response.errorMessage}")
                 tx = tx.copy(