I'm having trouble setting up my foreign key on my table, maybe I'm doing something wrong.

I am using a database management software, navicat. i have just setup my tables with all the fields and have already identified their respective primary keys, but i havent identified my foreign keys through the navicat yet.

what happens is that, when i try to create my foreign keys, i get an error from navicat that says something about my constraints. and i end up not being able to create my foreign keys.

i might have a system design flaw somewhere, but all i can think of is that maybe you cant use the primary key of a table as a foreign key of another table? because thats what i did.

create an index on the foreign key first