curl --request POST \
  --url https://api.unibee.top/merchant/discount/plan_apply_preview \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "code": "<string>",
  "email": "<string>",
  "externalPlanId": "<string>",
  "isChangeToLongPlan": true,
  "isChangeToSameIntervalPlan": true,
  "isUpgrade": true,
  "planId": 123
}'

{
  "code": 123,
  "data": {
    "discountAmount": 123,
    "discountCode": {
      "advance": true,
      "billingType": 123,
      "code": "<string>",
      "createTime": 123,
      "currency": "<string>",
      "cycleLimit": 123,
      "discountAmount": 123,
      "discountPercentage": 123,
      "discountType": 123,
      "endTime": 123,
      "id": 123,
      "isDeleted": 123,
      "merchantId": 123,
      "metadata": {},
      "name": "<string>",
      "planApplyGroup": {
        "currency": [
          "<string>"
        ],
        "groupPlanIntervalSelector": [
          {
            "intervalCount": 123,
            "intervalUnit": "<string>"
          }
        ],
        "type": [
          123
        ]
      },
      "planApplyType": 123,
      "planIds": [
        123
      ],
      "quantity": 123,
      "startTime": 123,
      "status": 123,
      "upgradeLongerOnly": true,
      "upgradeOnly": true,
      "userLimit": 123,
      "userScope": 123
    },
    "failureReason": "<string>",
    "valid": true
  },
  "message": "<string>",
  "redirect": "<string>",
  "requestId": "<string>"
}