Identifying ReCharge subscription through Carrier Service

Shopify Partner
39 1 4

We are offering our merchants shipping options through the carrier service callback URL.

Are there any known ways to detect when the shipping rate request sent to a carrier service is for a ReCharge subscription? We want to offer different rates based on whether the user is purchasing a subscription or not.

The checkout process is different when the customer is purchasing a subscription, the user actually checks out on this URL:

But the carrier service callback URL is requested, there is nothing to distinguish the rate as a subscription rate - the price is the same, the SKU is the same, the headers are the same, the JSON payload is identical. Since discounts aren't passed to the carrier service, it's not possible to detect a subscription based on a discount either.