Little Help with EDI and TN

We split in TN at the GS level. Im a little confused about something. Im fairly new at EDI and TN. I have a 4010 850 EDI document. The company is sending it to us. They use a different ISA and GS qualifier. Where does the TPA come in, is it at the GS or the ISA level considering we do the GS split? Im not sure who to make the trading partner agreement with the GS ID or the ISA ID?? The doc is basically inbound to us.

Thanks.

you should create EDITPA for the partner at ISA level, both partner ISA Id and ISAqualifier,once this is done you should create partner id and qualifier in partner profile to recognize GSA ID and GSA Qualifier.

Thanks,
VJ