I've been trying to add custom shipping methods to a Magento 2 webshop, using configurations in app/code/vendor/module/etc/config.xml, app/code/vendor/module/etc/system.xml and app/code/vendor/module/Model/Carrier/Shippingmethod.php.
So, this all works, and I can select the shipping methods. Also, when NOT logged in, the checkout works fine and can get completed.
The problem is, when logged in with a (new) customer, when using one of the custom shipping methods, it throws the following error: 'Please specify a shipping method' (freely translated from original language). The console throws the following error:
When I go the following link: http://mywebshop.com/rest/default/V1/carts/mine/payment-information
It says "User not authorized for %resources" and a tag with a few php files:
Some research later, people talk about tokens and stuff, but can't figure it out.