Does anyone have knowledge about the APN-OI parameter?

Hello Experts.

Does anyone have knowledge about the APN-OI parameter?

Can it be used to select a virtual APN on the PGW, or is it only for selecting a different PGW for users?

Our use case involves classifying VoLTE users and routing traffic to different P-CSCFs for various groups using the PCO configuration on the PGW.