Is it possible to fix a situation where someone has authorized a Sketchfab account via the Asset Store, but mistakenly used wrong email for Sketchfab verification? Now PlayCanvas seems to be connected to that Sketchfab account, which is created, but not verified (wrong, probably non-existent email).
This causes an error when trying to import any Sketchfab asset.
could you try to clear all cookies in the browser (for PlayCanvas.com and Sketchfab), create account on Sketchfab first, and try to link it from PlayCanvas after that? If it fails, share you ID on playcanvas please.