Hi,
The field LOKKT is Alternative Account Number in Company Code. It isn't reconciliation and can be filled in FS00.
Please follow below steps:
1 - enter FSS0 and flag Rec alt acc.
2 - Got to Field Status Change - OBD4 - Define Field Status group as optional for Rec alt acc.
3 - S_ALR_87002480 - Define Alternative Reconciliation Accounts.
Then you will be able to enter reconciliation account manually in FB01:
Best Regards