I am not able to create a submission using the https://www.formstack.com/api/v2/form/{id}/submission.json api

Request is
field_x: "field_136217866=testing"
read: false

Response is
{
"id": "1049882881",
"timestamp": "2022-12-22 12:56:53",
"user_agent": "Amazon CloudFront",
"remote_addr": "115.99.243.188",
"payment_status": "",
"form": "5095980",
"latitude": null,
"longitude": null,
"data": []
}