Contract &1 is blocked for billing, billing block reason &2

What causes this issue?

You tried to bill contract &v1&. This is not possible because the
contract is blocked from billing.

System Response

During billing, a billing block always terminates the procedure and
triggers an error message in the log.
In mass simulation, the billing block reason determines whether billing
is terminated with an error message, or whether a warning is issued
(field <DS:DE.MSIM_OK>billing block reason permits mass simulation</>)
In budget billing, the billing block reason determines whether billing
is terminated with an error message, or whether just a warning is issued
(field <DS:DE.BBP_OK>budget billing block reason permits budget billing
simulation</>)
For other types of billing simulation, a billing block just triggers a
warning in the log.
You can override the above rules using the Business Add-In
<DS:SIMG.ISU_BI_BLOCK_BILLING>ISU_BI_BLOCK_BILLING</>.

How to fix this error?

If you want to bill a contract, you must first of all release it for
billing. To do this, you must enter a corresponding release reason in
the contract.

Error message extract from SAP system. Copyright SAP SE.