Well, actually, PieFed.social has enabled it’s API which means that the app Interstellar can be used with it. Find out more about the app at https://interstellar.jwr.one/. iOS users can use the testing version at https://testflight.apple.com/join/JXRtHye2
https://feddit.online/, another PF instance, has enabled the API too and I expect others will follow in good time.
Sorry about that, it sounds very frustrating.
I’ve found that a field used to store account timezones was too short for yours. I’ve increased the size now so your next registration attempt will succeed.