In ERP/Ln trying to Close service orders which is completed but get error "Material not completely issued". Need some advise how to close it.

I suggest that you check warehouse manager dashboard for the service order. It seems likely that some steps have not been completed in the outbound (or inbound if any) warehouse process. Check the outbound status.

Yes, correct. Materials are not completely issues against Service Order. Execute all the warehouse orders against that Service order. This issue will be reolved.