Some users fail to refresh token, and the error message is as follows

[duodebuyali]

refreshAccessToken:{"errors":[{"errorType":"invalid_grant","message":"Refresh token invalid: f4f6cc469121a451108a1cebfcac8acf1bbe7a3868c76da936556ae614e9e650. Visit https://dev.fitbit.com/docs/oauth2 for more information on the Fitbit Web API authorization process."}],"success":false} 

[gmdev · Accepted solution]

Hello @duodebuyali.

You are probably facing the issue discussed in this post.