Service order fullfilment

Helo, i'm new to squarespace commerce and API, but i must say documentation is seriously lacking.

We have software downloads (that are hosted on our server) - there is no option to supply custom download url (so we don't need to upload files every time there is new version of software release), therefore i set product type to service instead.

i made test order, and want to do fullfilment trough API, but there is no documentation, only example is physical shipping with UPS ... which doesn't make sense for service.

when i try to call

POST https://api.squarespace.com/1.0/commerce/orders/{orderid}/fulfillments

i get 404 response, tried with shipments specified (from sample), with shipments empty, without shipments

i can get order details when calling 

GET https://api.squarespace.com/1.0/commerce/orders/{orderid}

so order exists.

i have no idea, how to clear order trough API, since there is no proper documentation or relevant examples, therefore if anyone knows, how this is done, any advice is welcome.