GSuite emails (firstname.lastname@example.org) on occasion have problems linking channels to TubeBuddy.com. They get a no channel found or access denied error.
1) Give a non GSuite email (email@example.com) channel manager rights to the channel using these instructions
2) Log in to TubeBuddy.com with the non Gsuite email account. Click the "Add Channel" button and select the Gmail account, then select the channel you want to link to TubeBuddy.