That's on the technical side, on the project side it was even worse, I had an earlier MVP to base my designs on while he (backend guy) had to deal with multiple basically hostile 3rd party vendors.
The predictable happened, after just 1 month it was 100% clear to me that it was impossible to work at the same pace, so I mocked up all the endpoints I expected, built most of the front-end and was done in 5-6 months, after multiple iterations with the previous business person who made the MVP. The backend (remember, 1 guy) had just gotten the Auth right basically, and almost nothing else in working conditions yet.
My manager reaction? He was pissed that I had done it against a mock API instead of the inexisting real one, told me to wait until the end-points were ready and integrate them and wouldn't give me any other work otherwise despite of my best arguments. What happened is during the next 3 months I was basically writing and rewriting the app, becoming very proficient in React. Then the manager started to hear heat from above, and he started to complain about my coworker in a very similar situation of this article, so I started to look for a new job. That backend coworker left few days after me and never came back (I was probably the only non-hostile one, even friendly, to him at work by that point).