This is the error that is printed as a result of the plugin invocation.
(I have replaced some parts with "variables", but the URL is correct. When i send it manually, a build is started.)

ERROR: Unexpected response from http://<jenkins-root>/view/<view-name>/job/<job-name>/buildWithParameters?token=<job-token>&PARAM1=value1&PARAM2=value2/api/json?tree=actions[parameterDefinitions],property[parameterDefinitions],name,fullName,displayName,fullDisplayName,url - status code 201

The problem seems to me that the plugin is just adding another path part to this URL. But the URL obviously contains parameters, the required token above anything else.
So just adding more path to it is always going to produce an invalid URL / unexpected response.