Filter error while using with schema

I have a query like this

select *
from mongodb.ACT a
where a.FUNDPROVIDER = 'BANK'

which is run successfully. But trying to use filter for the category and got error

select *
from mongodb.ACT a
where a.FUNDPROVIDER = {{fundprovider}}

here is the query preview

select *
from mongodb.ACT a
where a.FUNDPROVIDER = ("MONGODB"."ACT"."FUNDPROVIDER" = 'BANK')

Which fundprovider is a field filter on the same variable and table. And I've tried to select 1 and 2 categories in filter but got the same result as

ORA-00907: missing right parenthesis ORA-00907 - Database Error Messages

also when i use just {{a.FUNDPROVIDER}} still got the error. Could anyone help on this? Thanks