Welcome to the FreeAgent API forum! I’m Adam and I’m one of the Support Engineers here at FreeAgent.
Firstly, yes, you’re right in thinking that’s the URL to query if you want to get the trial balance totals.
Just to give a bit of background, the error that you’re getting back is as a result of the format of the Authorization header not matching “Bearer TOKEN”. If the Authorization header was missing, or the token was incorrect, you would get back a different error.
Can I clarify, are you seeing this error when querying the FreeAgent API via the Google OAuth 2.0 Playground or via Microsoft Flow? Just to help troubleshoot, are you able to query the trial balance URL successfully via curl? (Here is a page in our docs giving some guidance if you haven’t already given this a go - FreeAgent Developer Dashboard)