Error Message: 
“Error Redirect: URI Mismatch.
The redirect URL in this request: “XXXX” does not match the ones authorized for OAuth client.”

-This error message can happen when authorizing google drive account under A5 Documents Configuration tab and you have a custom domain setup in this org along with older package version installed.

How to resolve: 
Please go to AppExchange to upgrade your app package version to latest package available. After you upgrade your package version, then proceed back to A5 Documents Configuration tab to authorize app with your chosen google drive account and error should no longer be there.