"Unable to link to this account" error message

Last Updated: 03/26/2018
This is working as intended.

If you receive the "unable to link to this account" message when attempting to link a login provider to your account, it is often because that Facebook or Google account is already linked to another Pokémon GO account. This is the intended functionality to prevent multiple Pokémon GO accounts from using the same login credentials. 

In a future release, we will update the error messaging to provide more details on what causes this issue.