Invalid_grant

Invalid_grant error has two common causes.

1. Your server’s clock is not in sync with NTP. (Solution: check the server time if its incorrect fix it. )
2. The refresh token limit has been exceeded. (Solution: Nothing you can do they cant have more refresh tokens in use) Applications can request multiple refresh tokens. For example, this is useful in situations where a user wants to install an application on multiple machines. In this case, two refresh tokens are required, one for each installation. When the number of refresh tokens exceeds the limit, older tokens become invalid. If the application attempts to use an invalidated refresh token, an invalid_grant error response is returned. The limit for each unique pair of OAuth 2.0 client and is 25 refresh tokens (note that this limit is subject to change). If the application continues to request refresh tokens for the same Client/Account pair, once the 26th token is issued, the 1st refresh token that was previously issued will become invalid. The 27th requested refresh token would invalidate the 2nd previously issued token and so on.