Test Plans API - Create Test Plans

Question

Hello,

I'm trying to create a test plans through the Azure DevOps API 6.0.

I'm using a personal access token.

Request :
fetch(https://dev.azure.com/${organization_name}/${project_name}/_apis/testplan/plans?api-version=6.1-preview.1, {
"method": "POST",
"headers": {
"Authorization": {{fetch_headers_authorization}},
"Content-Type": "application/json"
},
"body": {
"name": "test_azure_api",
"areaPath": {{project_name}}\\QA,
"iteration": {{project_name}}\\4.37
}
})

Response :
{
'$id': '1',
innerException: null,
message: 'TF400898: An Internal Error Occurred. Activity Id: 0f7b1add-78c3-4f5f-86a4-b1027f1d839d.',
typeName: 'Newtonsoft.Json.JsonReaderException, Newtonsoft.Json',
typeKey: 'JsonReaderException',
errorCode: 0,
eventId: 0
}

Can you please tell show me an example of a working fetch request for that purpose.

Please, can you alse indicate what's the mandatory input in the body request.

Best Regards.