GSuite emails (email@example.com) 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 (firstname.lastname@example.org) channel manager rights to the channel using these instructions
2) Log in to TubeBuddy.com with a non Gsuite email account. Click the "Add Channel" button and select the Gmail account, then select the channel you want to link to TubeBuddy.