In case you have customizations on SO301000 screen, first try to unpublish them all and check if all your so lines (under Details TAB) have the complete checkbox field checked, if yes, you can try to reopen the SO and close complete the same Sales order or manually complete the checkboxes. If the above actions don’t work, please can contact your VAR, they may need to raise a ticket with Acumatica for further investigation.