Hi,
As Unaccepted service entry sheet created for your service, follow any one option.
Option-1
If SES( service entry sheet) created and released, then follow the process
1. Reject the release of SES by revoking in ML81N
2. Now DELETE the SES in ML81N
Option-2
If SES( service entry sheet) only created then follow the process
1. EDIT the SES in ML81N
2. Now DELETE the SES in ML81N
From above , select one option based on SES nature- then only you can set deletion flag to the line item in Service PO in ME22N.
Regards,
Biju K