The budget line types in commitment item and cover pool are different

What causes this issue?

The commitment item which you would like to assign to the cover pool
&V1& has a different budget line type than the other commitment items
which were already assigned to the cover pool.

System Response

Entry is not accepted.

How to fix this error?

Assign only commitment items with the same budget line type to the
cover pool.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.