@Gargron As addition for people trying this: Sometimes, the old server happens to have old data fetched. This means, it doesn't have the newest account data of the new account. This might result in the error that the new account doesn't properly refer back to the old one.

In this case, do a simple search for your user URL(!) (e.g. https://chaos.social/@esureL) to update the data and then try again. :)