zpay32: add support for P2TR fallback addresses

zpay32/encode.go

@@ -202,13 +202,15 @@ func writeTaggedFields(bufferBase32 *bytes.Buffer, invoice *Invoice) error {
 		var version byte
 		switch addr := invoice.FallbackAddr.(type) {
 		case *btcutil.AddressPubKeyHash:
-			version = 17
+			version = fallbackVersionPubkeyHash
 		case *btcutil.AddressScriptHash:
-			version = 18
+			version = fallbackVersionScriptHash
 		case *btcutil.AddressWitnessPubKeyHash:
 			version = addr.WitnessVersion()
 		case *btcutil.AddressWitnessScriptHash:
 			version = addr.WitnessVersion()
+		case *btcutil.AddressTaproot:
+			version = addr.WitnessVersion()
 		default:
 			return fmt.Errorf("unknown fallback address type")
 		}