We'll be using Bandcamp's partner system to do the authorization which requires some manual steps.
Invite us as a partner within Bandcamp by going to the Merch Orders section and accessing the partner invite tool. When it asks for partner email, please enter:
Reach out to support to let us know you've sent the partner invite
We'll accept the invite and add your Bandcamp account on our end. Once that's done, when attempting to create your Bandcamp sales channel again, you should now see your Bandcamp account connected