Hi
Is your GL Account created as a cost element, that it will post to a cost center? There are multiple ways in which cost center can be derived:
1. If you are on ECC, you can assign a default cost center in T Code KA01
2. If you are on ECC, you can also assign a default cost center in T Code OKB9 for your company code
3. If you are on S/4 HANA, the cost center assignment is done in OKB9
4. If the GL is posted against a sales order with a reason code, the cost center can be derived through OVF3
5. You may also have a substitution rule for populating cost center, which can be done through GGB1 as well.
You need to check how the cost center is populated and what kind of posting is happening and take one of the steps mentioned above
Thanks & Regards
Sanil Bhandari