[FIX] pos_payment_terminal: reject cancellation

Since we can't cancel the transaction, we return a rejected
promise. The user should cancel manually which will
effectively free the transaction and let the user delete it.

pos_payment_terminal/static/src/js/payment_terminal.js

@@ -25,12 +25,12 @@ odoo.define("pos_payment_terminal.payment", function(require) {
 
         send_payment_cancel: function() {
             this._super.apply(this, arguments);
-            this._show_tip(
+            this._show_error(
                 _t(
-                    "Cancel the transaction by pressing the red button on the payment terminal."
+                    "Please press the red button on the payment terminal to cancel the transaction."
                 )
             );
-            return Promise.resolve();
+            return Promise.reject();
         },
 
         _oca_payment_terminal_pay: function() {
@@ -185,14 +185,6 @@ odoo.define("pos_payment_terminal.payment", function(require) {
                     body: msg,
                 });
         },
-
-        _show_tip: function(msg, title) {
-            if (!_.isEmpty(this.pos.gui.popup_instances))
-                this.pos.gui.show_popup("alert", {
-                    title: title || _t("Payment Terminal"),
-                    body: msg,
-                });
-        },
     });
     return OCAPaymentTerminal;
 });