[Rest API] Client and POST request with Processing .net libraries

I want to send a POST request to ThingWorx REST API to access my thingworx server.
I am able to send the POST request with HTTPIE to my thingworx server but with processing I am not able to do this and I don’t understand understand where is the issue.
I thinks it is when i am using write fonctions with my client but I have no clue to solve this.

I will look for POSTman it is not the first time I heard this name. I found it many time during my research.