Packix now has a DRM API that tweak developers can hit from their servers to verify purchases for DRM reasons. You will need to send the package identifier (com.author.tweakname thing), device UDID, device Model (like iPhone7,2) and a developer access key you have generated in the Packix Developer Portal under "Developer->Keys". You should always use your server as an inbetween with the packix DRM API as to not reveal your developer access key that you generated.
POST https://repo.packix.com/api/drm/check
: Get Information on whether the UDID and Device Model own the package