curl -X POST "https://api.erp.tr/api/v1/arac/qr" \
  -H "Content-Type: application/json" \
  -d '{"text":"https://erp.tr"}'

using var http = new HttpClient();
var resp = await http.PostAsJsonAsync("https://api.erp.tr/api/v1/arac/qr",
  {"text":"https://erp.tr"});
var json = await resp.Content.ReadAsStringAsync();