: app{.}swaggerhub{.}com/apis/d_yo_r/gainium_openapidoc.yml
This can help to create client (and server) code for different languages. It can be easily extended and validated here.
What doesn’t work here, is to try the endpoints. That should be done via Gainium’s API homepage as it internally intercepts the input on the client side to calculate the appropriate signature on-the-fly.