offer_read_only
Status 409. This rule is not one the API changes.
What it means
The rule was set up in a way the API does not change: it is not a campaign, a product offer or a channel offer. GET /stores/{store_key}/programme/offers lists it as other. Nothing was changed.
What to do
Change or remove it in the Matrix Rewards app in your Shopify admin.
Safe to send again?
No. The same request will get the same answer.
Where you can meet it
POST /stores/{store_key}/programme/offers: Add an offer: a campaign, a product offer or a channel offerPOST /stores/{store_key}/programme/offers/{offer_id}: Change an offerPOST /stores/{store_key}/programme/offers/{offer_id}/remove: Remove an offer
Every code, and the shape of an error answer: Errors.