fix #4219

gui/qt/main_window.py

@@ -1838,6 +1838,9 @@ class ElectrumWindow(QMainWindow, MessageBoxMixin, PrintError):
 
     def show_invoice(self, key):
         pr = self.invoices.get(key)
+        if pr is None:
+            self.show_error('Cannot find payment request in wallet.')
+            return
         pr.verify(self.contacts)
         self.show_pr_details(pr)
 

lib/paymentrequest.py

@@ -453,7 +453,11 @@ class InvoiceStore(object):
 
     def set_paid(self, pr, txid):
         pr.tx = txid
-        self.paid[txid] = pr.get_id()
+        pr_id = pr.get_id()
+        self.paid[txid] = pr_id
+        if pr_id not in self.invoices:
+            # in case the user had deleted it previously
+            self.add(pr)
 
     def load(self, d):
         for k, v in d.items():