Having already an Integration Variant, you should now assign it to a Company Code. You could use one integration variant to several company codes.
IMG Path: Financial Accounting (New) -> Financial Accounting Global Settings (New) -> Ledgers -> Real-Time Integration of Controlling with Financial accounting -> Assign Variants for Real-Time Integration to Company Codes
When you open the transaction, you will see a list of already assigned integration variants to company codes. Create a new entry to assign it to the newly created company code.
Assign the Variant that you wish to your company code.