curl --request PUT \
  --url https://api.gcore.com/billing/v3/trials/{trialId} \
  --header 'Authorization: <api-key>' \
  --header 'Content-Type: application/json' \
  --data '{
  "days_limit": 123,
  "options": [
    {
      "internal_name": "CDN_TRIAL_TRAFFIC_LIMIT",
      "value": 300
    }
  ]
}'

{
  "id": 123,
  "client_id": 123,
  "client_company": "Client Company",
  "product_id": 123,
  "product_internal_name": "CDN",
  "product_name_en": "CDN",
  "plan_id": 123,
  "plan_name_en": "Plan name",
  "days_limit": 123,
  "started_at": "2023-11-07T05:31:56Z",
  "ended_at": "2023-11-07T05:31:56Z",
  "created_at": "2023-11-07T05:31:56Z",
  "options": [
    {
      "id": 123,
      "trial_id": 123,
      "feature_id": 123,
      "name_en": "Trial traffic volume",
      "description_en": "Traffic volume given to a client during the trial.",
      "internal_name": "CDN_TRIAL_TRAFFIC_LIMIT",
      "unit_id": 123,
      "value": 300,
      "is_limit": true,
      "used_value": "124,00000000",
      "feature_name_en": "CDN-HTTP/HTTPS Delivery (GB)",
      "unit_name_en": "GB",
      "updated_at": "2023-11-07T05:31:56Z"
    }
  ]
}