All GET endpoints on the API support oData query syntax. This syntax is a common standard and more information is available here.
If you wish to query a given endpoint (subscriptions in this case) based on a given attribute, you can use the API as the following example outlines:
GET https://api.upodi.io/v2/subscriptions/?$filter=CustomerID eq guid'0b5e2a3f-9845-4efb-a96d-2e20c04c7140' HTTP/1.1
curl
-H "Content-Type: application/json"
-H "Authorization: Bearer <base64 key>"
https://api.upodi.io/v2/subscriptions/?$filter=CustomerID eq guid'0b5e2a3f-9845-4efb-a96d-2e20c04c7140'