Manual reservation &1 is present only in ECC

What causes this issue?

Manual reservation is present in the ECC system but missing from the APO
system due to either of the following reasons:
The manual reservation was originally created in APO but has since been
deleted. However, this information has not been sent to ECC.
The manual reservation was originally created in ECC but was not created
in APO because of a system error.

System Response

The CCR tool is unable to find the reservation in the APO system.

How to fix this error?

If the manual reservation was created in APO and later deleted, then
manually delete the reservation from ECC.
If the manual reservation was created in ECC but not in APO, then
reconcile the reservation by choosing the Send to APO button.

Procedure for System Administrators

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.