Change Zip Code in A/R Account-Zip Code doesn't exist. Zip Code is in Library Master Setup

SOLVED

Sage 100cloud Standard 2020 Ver. 6.20.0.1

(Zip Code in question 95037-Morgan Hill, Ca)

When I attempt to change the zip code for a customer in the A/R Customer Maintenance module, I receive a message:

Is this a new Zip Code?

When I select No, Sage will not allow me to change the zip code (reverts to previous zip code.)

When I go to Library Master/Setup/ZIP/Postal Code Maintenance and enter the zip code the fields are populated (hence the "No" answer above)

(If I select "Yes" for the new zip code question, I am presented a form with blank fields to complete)

Am I missing something?

How do I get the new zip code in for the customer without duplicating the zip code in the database...?