how to check which Contract Registration Code was used for a device

Hello
Indeed; log in in your forticloud portal, locate your assets
When you edit a product, fortigate, analyzer etc, you should see a widget named "Entitlement"
Open it and you should see all contracts applied to that unit. contract number, sku, and dates

hope it helps

Use the forticloud portal, but you have certain that use the same account to registre asset then.