I tested it on a dummy file and it worked

are you sure you didn't key it in incorrectly - maybe add an extra zero?

Isn't it now called BOM, "Bank of Mexico?"

I tried it and it did not work.  Maybe double check with your client?  I googled routing numbers for BOA and that was not an option.  

I googled boa routing number and typed it out and it came back as a california routing number for bank of america

maybe ask client to provide a copy of the check to confirm? or do they have another bank account?

Savings account vs checking account?

Or did the routing number come from a deposit slip instead of a check?

I've found there can be differences...

BOA took over another bank and client never got new checks - Tell client to get the new routing number

State-Specific or Legacy Routing Numbers

Although Truist leans on a single routing number (061000104) for most activities, some accounts still use older codes from BB&T. These codes vary based on the state where the account originated. For instance:

• Florida: 263191387

• North Carolina: 053101121

• Virginia: 051404260

It’s a good idea to confirm your exact routing number if your account dates back to BB&T. You can contact Truist support or refer to account documentation if you suspect a state-specific number still applies. As a side note, if you’d like to see how other big banks handle varied routing systems, check out Bank of America Routing Numbers in the US (Complete Edition).

This danged keyboard has the capital O way too close to the zero.  

The problem might be that the taxpayer has checks that were printed 27 years ago, when Bank of America was a California bank.