Set your logging RESTConsume to trace so you can see in your console what goes over the line. This way you can see the response from the other side. Then check you import mapping.
Regards,
Ronald
The error message says the JSON you are trying to import starts with ‘<‘, and that is invalid.
It could be that XML or an HTML error message is being returned from your REST call.
As Ronald suggests, setting the log level for REST Consume to trace will show the contents of the REST calls in your log files, and should show what is going on.