Once connected, each transactions you export will post as a journal entry. You'll want to verify first what those transactions are and check also the mapping. All transactions should reflect into the appropriate accounts based on how you map it.
You can also ask an assistance from Brex so they can check if how you set it up is correct.
Reply below if you need further assistance. I'm here to help.
I'm reaching out to BREX for answers - waiting for a replay.
In their setup screen there is a field to identify an Accounts Payable. I'm not sure what to do with this. I suspect that I should I set up a unique AP called BREX AP and that all the imported transactions will populate it.
Then, when I post the summary (monthly) debit from my bank account, it will also post to this account and it will reconcile.