What I think it should be:
(as part of a SELECT statement, this is one of the columns):
IIF(1=1, 'MX', 'NA') AS shippercountrymapcode
Note: 1=1 will be changed to correct test after issue is resolved
What SSMS keeps suggesting is should be:
Select IIF('1=1', 'MX', 'NA') AS shippercountrymapcode
It adds the quotes on 1=1 and produces an error
An expression of non-boolean type specified in a context where a condition is expected, near'('.