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Could you provide some more information on where you see this message? The only thing I can think of this showing up is if the account linking provider you are using has something called a "master email" and requires it for login.
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Account linking but no access token after a day
Taking address as input from user
Alexa account linking with oauth 1 service
How to link my Echo Dot to laptop to do skills (beginner)?
The blue light ring is still flashing after response.tell