Error Code: 2124-0291
When attempting to transfer a User Account from one Nintendo Switch console to another, an error code is displayed.
Additional Information:
It is possible for a Nintendo Account to be linked to more than one Nintendo Switch console.
While transferring a User from one Nintendo Switch console to another, if the Nintendo Account used in this process is already linked to a User on the target console, an error code will be displayed and the transfer will not be able to continue.
What to Do:
Unlink the Nintendo Account from the User on the target console, then start the user and save data transfer again.