we have the web services almost exclusively on-prem and now getting on to power apps platform.How do you consume a web service deployed on-prem via Power BI online platform?

we have the web services almost exclusively on-prem and now getting on to power apps platform.How do you consume a web service deployed on-prem via Power BI online platform?
I use the On-premises data gateway to connect to my on-prem resources. Works like a charm. But, so far, I only used it to access on-prem sql servers and files on our old file servers.
Documentation says it should also be able to access on-prem API's etc.
Tried that allready?
https://powerbi.microsoft.com/en-us/gateway/
Kind regards,
Maurits