diff --git a/electrum/gui/qt/main_window.py b/electrum/gui/qt/main_window.py
index 8c684d60d..7cbb98383 100644
--- a/electrum/gui/qt/main_window.py
+++ b/electrum/gui/qt/main_window.py
@@ -148,6 +148,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         self.app = gui_object.app
         self.cleaned_up = False
         self.payment_request = None  # type: Optional[paymentrequest.PaymentRequest]
+        self.payto_URI = None
         self.checking_accounts = False
         self.qr_window = None
         self.not_enough_funds = False
@@ -1734,9 +1735,8 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
         elif invoice['type'] == PR_TYPE_ONCHAIN:
             message = invoice['message']
             outputs = invoice['outputs']
-            amount = sum(map(lambda x:x[2], outputs))
         else:
-            raise Exception('unknowwn invoicce type')
+            raise Exception('unknown invoice type')
 
         if run_hook('abort_send', self):
             return
@@ -1760,7 +1760,7 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, Logger):
             self.show_message(str(e))
             return
 
-        amount = tx.output_value() if self.max_button.isChecked() else sum(map(lambda x:x[2], outputs))
+        amount = tx.output_value() if self.max_button.isChecked() else sum(map(lambda x: x.value, outputs))
         fee = tx.get_fee()
 
         use_rbf = bool(self.config.get('use_rbf', True))
diff --git a/electrum/util.py b/electrum/util.py
index 724039b21..9f6a9683d 100644
--- a/electrum/util.py
+++ b/electrum/util.py
@@ -585,12 +585,14 @@ def format_satoshis_plain(x, decimal_point = 8):
     return "{:.8f}".format(Decimal(x) / scale_factor).rstrip('0').rstrip('.')
 
 
-DECIMAL_POINT = localeconv()['decimal_point']
+DECIMAL_POINT = localeconv()['decimal_point']  # type: str
 
 
-def format_satoshis(x, num_zeros=0, decimal_point=8, precision=None, is_diff=False, whitespaces=False):
+def format_satoshis(x, num_zeros=0, decimal_point=8, precision=None, is_diff=False, whitespaces=False) -> str:
     if x is None:
         return 'unknown'
+    if x == '!':
+        return 'max'
     if precision is None:
         precision = decimal_point
     # format string
diff --git a/electrum/wallet.py b/electrum/wallet.py
index 8a14d28a8..8c77bd2f2 100644
--- a/electrum/wallet.py
+++ b/electrum/wallet.py
@@ -512,8 +512,11 @@ class Abstract_Wallet(AddressSynchronizer):
                 'txpos_in_block': hist_item.tx_mined_status.txpos,
             }
 
-    def create_invoice(self, outputs, message, pr, URI):
-        amount = sum(x[2] for x in outputs)
+    def create_invoice(self, outputs: List[TxOutput], message, pr, URI):
+        if '!' in (x.value for x in outputs):
+            amount = '!'
+        else:
+            amount = sum(x.value for x in outputs)
         invoice = {
             'type': PR_TYPE_ONCHAIN,
             'message': message,