MX Merchant Ideas

We are a new customer, just starting to use the MX Merchant virtual terminal. Our previous FD50 terminal required that we enter PO Box addresses by using the alpha button. We entered POBOX1234 without any spaces, and that PO Box (with a correct zip code) would return a YYY authentication. We have been trying different ways to do this in MX Merchant, but have not yet found the right way. Part of the reason may be that address line 1 requires at least 5 characters. When we enter PO BOX 1234, or 1234 PO BOX, or POBOX1234 the numerals 1234 do not populate the address field when we select the credit card in the Quick Pay screen. Is there a way to enter PO Box addresses so they automatically populate the address field in QuickPay. Thank you.