Wimpy App technical issues

I was at Wimpy Riversquare with my 2 children, ladies at the door were friendly and offered us the table for 3,our waitress was Priscilla who offered best service because she introduced the wimpy app to us which she explained that first time user or registration you get a free milkshake, the problem started where our apps all three of us could not generate the discount on our milkshakes, then our waitress called the store manager for assistance which two of them were very friendly i couldn't get their names but very helpful and professional But Jolanda whose name tag written AREA MANAGER ,her service was not that of an area manager, firstly she could not believe that we were the first time user on the app because of the issue we encountered, I explained that the reason we opted for the meal we ordered was because of free milkshake, there was no way I could take my chances on getting the free milkshake if I knew that I have benefited before, worst part she left us there at the shop without the issue being resolved, she did not even bother to come to us and tell us she was leaving, she left the manager with the unresolved matter, I am not happy with how she handled the issue that was on hand It is my request that the innovation teams should come with solutions as well if the app they introducing to us is not functional or have technical issues, because the managers were sent from pillar to post to resolve our matter