Ebay REST API and error 25007 when publishing

THIS(!!!11) took me hours of figering out (maybe it's written somewhere in the docs and I've read over it). So, the API itself is pretty straight forward: create an inventory item, create an offer based on that item and finally publish the offer. To specify the terms of the offer you're asked to set the payment, return and fulfillment policies. Generally there's one payemnt and one return policy set for your user but multiple fulfillment policies. Now, when starting with the whole REST API stuff you may notice that you're not allowed to list the payment and return policies and this is exactly the hint which leads to the 25007 "You have so specify at least one shipping service" error when trying to publish you newly created order. To solve this, just run the optIn on the SELLING_POLICY_MANAGEMENT program via Account API v1 especially https://api.ebay.com/oauth/api_scope/sell.account. After opting in I was able to publish the offer which previously already worked in the sandbox!