use mempool utxo for transactions

lib/g1/api.dart

@@ -568,7 +568,7 @@ Future<PayResult> pay(
     {required String to,
     required double amount,
     String? comment,
-    bool? useMempool}) async {
+    bool useMempool = false}) async {
   try {
     final SelectedGvaNode selected = getGvaNode();
 
@@ -584,7 +584,7 @@ Future<PayResult> pay(
           amount: amount,
           comment: comment ?? '',
           cesiumSeed: wallet.seed,
-          useMempool: useMempool ?? false,
+          useMempool: useMempool,
           raiseException: true);
       logger('GVA replied with "$response"');
       return PayResult(message: response, node: selected);

lib/ui/pay_helper.dart

@@ -88,7 +88,10 @@ Future<void> payWithRetry(
           return;
         } else {
           final PayResult result = await pay(
-              to: contactPubKey, comment: comment, amount: convertedAmount);
+              to: contactPubKey,
+              comment: comment,
+              amount: convertedAmount,
+              useMempool: true);
           final Transaction pending = tx.copyWith(
               debugInfo:
                   'Node used: ${result.node != null ? result.node!.url : 'unknown'}');