Chain and branch: two different identifiers, two different jobs
The Yemeksepeti connection has two identifier concepts, and confusing them leaves the setup half-finished. The chain identifier represents your business as a whole and appears inside every API path; it is required. The branch identifier points to a single location and is needed for pulling orders, listing products and handling categories. The chain identifier establishes the connection, but without the branch identifier the daily flow does not work.
There is also a secret token for order notifications, and you do not generate it: it is created automatically when the connection is established. Seeing it empty on the setup screen is normal.