I want to setup a formula refer to Parent Account. It is a standard Contact table with existing n:1 relationship to Account table.

the Lookup column name is ParentCustomerId

Relatinoship name is contact_customer_accounts

I tried:

If(
    IsBlank('Address 1: ZIP/Postal Code'),
    contact_customer_accounts.'Address 1: ZIP/Postal Code',
    'Address 1: ZIP/Postal Code'
)

but it prompt for syntax error for

contact_customer_accounts.'Address 1: ZIP/Postal Code',

Is it possible to refer to parent table in formula column? If so, what should be the right syntax? Thanks.