My first thought is that you’re running the command in the wrong directory.
I’m not sure this has anything to do with the fact that you renamed the dev branch, but maybe try going through this process without that step.
Here is a forum post that goes through handling multiple remote repos: (Unofficial) Anvil Version Control for Dummies
Here is a guide for anvil extras that takes you through a process of taking an anvil app from a local git repo and pushing it to a blank anvil app (in this case the anvil extras app): Installation — Anvil Extras documentation