I was able to get this working. I believe the fix was logging into the bank's website and setting my account for the "main quicken account".

I did this via "customer service" -> "settings" -> "manage profiles" -> click the account for "quickbooks default"

I get the following error:

13:08:33 Sending request...
13:08:33 Using GnuTLS default ciphers.
13:08:33 TLS: SSL-Ciphers negotiated: TLS1.2:ECDHE-RSA-AES-256-GCM:AEAD
13:08:35 Waiting for response...
13:08:36 Parsing response...
13:08:36 Parsing response
13:08:36 Status for signon request: General error (Code 2000, severity "ERROR")
Error other than those specified by the remaining error codes. (Note: Servers should provide a more specific error whenever possible. Error code 2000 should be reserved for cases in which a more specific code is not available.)
13:08:36 Status for account info request: General error (Code 2000, severity "ERROR")
Error other than those specified by the remaining error codes. (Note: Servers should provide a more specific error whenever possible. Error code 2000 should be reserved for cases in which a more specific code is not available.)
13:08:36 Operation finished, you can now close this window.

for the following settings (default pulled via gnucash):
Regions Bank (Post 2016)
261170740
13131
Identity-RFG
https://onlinebanking.regions.com/Ofx/process.ofx