Is the Authorize.net Merchant Authorization the same thing as the Transaction Key? I do not see a merchant authorization on the Auth.net site, but I do see an API Key and Transaction Key.
Yes, they're the same, authorize.net renamed this (hover the "i" info field of CBSubs backend for the explanation)
Thanks for the valuable feedback through your founded question:
Making it a note here that this should be more visible in upcoming CBSubs 1.1.