Sorry, I got your question now. I misread your message and thought you want to reset the cleared items that were already cleared by FAGL_ACTIVATE_OP.
Adding more complexity to the situation, looks like you also have ledger group specific postings. If there are any ledger group specific postings, SAP recommended to reach out them directly. However, looks like since it was already messed up by activating the OI indicator directly from GL and not sure if SAP can help in this regard.
I would think better to create a new GL with correct settings and perform the transfer. I am not sure if it creates more complicated if you try to clear all the current open items and reset the OP indicator in GL directly again and then try to perform through FAGL_ACTIVATE_OP.
Regards,
Srinath