Jasper server how get the parameters from the ReportExecutionRequest in jasper studio - jasperserver

Question

I sent a ReportExecutionRequest to my jasper server CE, with one param into the ReportParameters list of ReportParameter.
The report parameter is like this:
ReportParameter{name='DOSSIER'limit='null'offset='null'select='null'criteria='null', values=[35201]}
after this is use this method to send the data to my jasper server:
return service.post()
.uri(builder -> builder.pathSegment("rest_v2", "reportExecutions").build())
.cookie(JSESSIONID, sessionId)
.bodyValue(reportExecutionRequest)
.exchangeToMono(response -> JasperServerResponse.fromBody(response, r -> r.bodyToMono(ReportExecution.class)))
.block(timeout);
Now I would like to use the param in jasper studio so I created a param named $P{DOSSIER} but for the post in my application the param is always null.
I did a try to post directly the value from postman to the server with this body and it works:
{
"reportUnitUri": "/applicationname/reportname",
"async": false,
"outputFormat": "pdf",
"parameters": {
"reportParameter": [
{
"name": "DOSSIER",
"value": [
15236
]
}
]
}
}
The only différence is the value without "s" into the reportParameter.class and my post request body but I used the reportParameter.clas from the jasper repository so I wonder how I could solve this.
Have you an idea?
Thanks in advance for your help