API get token receives error code 40002

[Issue Description]

When testing P-serise PBX API in PHP using CURL to POST request and trying to get a token, you might get the error as below:

{"errcode":40002,"errmsg":"PARAMETER ERROR","invalid_param_list":[{"field":"user_agent","validation_type":"required"}]}

[Cause]

Missing 'user agent' 

[Solution]

Please add a 'User-agent', you can set the value what you like.