Sorry about that. Piefed just had a new version release last week and part of that included some changes to the api that mobile clients use. Boost has been a bit slower to update than some of the others. It's unfortunate really, because Boost is my favorite mobile app for lemmy, but the updates can be slow. The good news is that we aren't planning any more breaking changes to the api going forward, so once Boost is updated, it should continue working.
As an aside, I would also recommend trying piefed as a PWA. It is my preferred way of using it on a mobile device.