Problem with A/P AAI selection

What information in an A/P Voucher and/or Payment is used to choose the AAI for the A/P Bank Account (PB)?

We are importing Voucher and Payments from a 3rd-party Application which creates E1 Invoice and Payment Journals, respectively
We need the vouchers to use the G/L Bank Account ending .905 versus our default .900.

We are relatively new to E1 on version 9.1

We setup the AAI 'PBNEWB' in 4.015, which is where our default AAI resides, specifying the appropriate Company,
the required Business Unit and Object, along with the required Subsidiary '.905'.
We also added 'NEWB' to UDC 41/9

On the Voucher we populated the G/L Offset with 'NEWB'.

When we post the Invoice and Payment Journals, the system uses the G/L Bank Account .900.

We also created the AAI of 'PCNEWB' which pointed to our 'default' A/P Trade Account to see if
it was needed to have the correct PB AAI found, but received the same result.

The only reply we get from the 3rd-party vendor is that ' it is a problem with you AAIs' and cannot tell us what we are missing.

see below from the Accounts Payable implementation guide:

Payables Bank (PB)
An AAI item for the default bank account (PB) is required. This item specifies the default bank account that
the system assigns if you do not enter a bank account number when you enter a voucher.
If you have multiple bank accounts defined for a company, you can define an offset using PByyyy (payables
bank account). If you use PByyyy, you must also define PCyyyy (payables trade account) for the same offset.
For example, company 1 has two bank accounts: 1.1110.BEAR and 1.1110.FIB. You define PBBEAR and
PBFIB to point to the respective bank account. PCBEAR and PCFIB must also exist in the AAI table. You
can, however, point them back to the same account defined in PC yyyy. In voucher entry, you would enter the
yyyy into the G/L Offset field in the detail area to specify an account.
For example, Universal Incorporated must be paid from OMNI National Bank, which is not the default
payables bank. Set up the GL offset code of OMNI in the supplier master record or on each voucher for
Universal Incorporated and set up these AAIs:
Item Description Co BU Obj Sub Seq No.
PBOMNI
(PByyyy)
OMNI bankspecific
code
Blank 100 1110 OMNI 4.015
PCOMNI
(PCyyyy)
OMNI bankspecific
GL
offset code
Blank 100 4110 Blank 4.020

Thank you for your reply