passing value between 2 files

I have 2 database files: Clients and Contracts.

After I fill in the customer's detail on Clients file, I want to create a new record on Contracts file and auto fill in the CustomerID and full name.

I set variable at Clients:
Set variable[$$customerID; Value:Clients::customerID]
Set variable[$$fullname; Value:Clients::fullname]

On the Contracts:
Set Field[Contracts::customerID;$$customerID]
Set Field[Contracts::fullname;$$fullname]

But the Contracts customerID and fullname fields are blank, it cannot pass in the variables. How to pass value between files?

Thanks for your help.

Regards,
Kevin