I tried to consume it using as per documentation but have no luck so far.
(1) tried the webservice using Postmand (works)
(2) try using BMOnline with same parameters
2 headers parameters
Key : Authorization
Authorization : Content-Type
1 body parameters
Json path : $
Data Type : text
is Array : No
Value : <copy from Postman raw body>
but it keep replying response 400
{"error":{"code":"BadArgument","message":"Invalid argument provided.","details":[{"code":"InputMismatchError","target":"input1","message":"Input data does not match input port schema."}]}}
You should deploy an application on-site, create a web service call and test network via fiddler to see what request is sent to web service. The message you've got means that bpm'online sends a request in a format that differs from that you are expecting. Then you can set up parameters in a such way that will fit to Azure learning standard.
The other option will be creating a script task with calling that webservice from c# code. If you are a developer this is the best way because allows you to do more than built-in web service call.