We've made some changes to the way we do object identifiers in the v2 version of our API. Whenever you get back a successful response from us that contains an object in it, we will return our new identifiers (id) in the response. Please use these identifiers for all your requests using the v2 API endpoints and beyond.
We will still support you sending us the old identifiers in your requests for a period of time but you should change to our new identifiers ASAP. The way we used to do identifiers has the risk of breaking your application if a shop deletes their API keys. In order to avoid this scenario, you should update the identifiers you use as soon as you can.
All of our new identifiers adopt a new convention where we use a prefix at the beginning of them to match the object they identify. For example, all subscriber ids will include a s_ prefix for their ids. This is how you can spot whether or not you are using these new ids or our old ids, whether or not they have a prefix at the beginning of it.