Replying to @Angel_T, the issue is not with my email spam email folder or the contact information that my vendor (the QB merchant) has on file for me.  I know this for a fact because:

   1) I have (and continue to) successfully received the vendor's QB-generated invoices they have sent me over the past several years.  These emails are being transmitted to me by the QB Payments email server.

   2) I have always gotten payment confirmation emails from the QB Payments service every time over the past several years, except until the QB Payments platform began blocking my bank account.

   3) I checked my spam folder anyway, as no email from QB Payments, Inuit, etc. was in there.

So since no declination error emails are being sent to myself (the payor) or my vendor (the QB merchant), how am I or my vendor supposed to determine the applicable R## error code?

Furthermore, even if were were able to ascertain the applicable R## code and thus know the appropriate action according to the 2nd article (Fix rejected ACH payments or fees in QuickBooks payments), then if a bank letter were "required" (assuming my bank is willing to waste their time with that), how/where would I submit said bank letter?  The article provides no contact information.  No email address, no contact form with an attachment upload capability, no postal mailing address.

Can you please investigate and advise on the appropriate R## code?  And if a bank letter is "required", can you please provide the contact information for the QB Payments team group or department to which said letter needs to be submitted?

Thanks!