For a successful top-up, you must specify in the body of the request

Parameter	Required	Description
invite_url	yes	Link for quickly adding a Steam user as a friend
package_id	yes	id of a specific game edition, obtained in Get Game By App ID for a specific game edition
region	yes	The recipient's region to which the game should be sent
reference	no	your ID , if necessary

If you follow the above rules, you will receive a response like this:

{
  "transaction_id":"uuid",
  "status": "pending",
  "error_code": 0
}

{
  "status": "success",
  "error_code": -1
}

{
  "status": "pending",
  "error_code": 0
}

"status" - transaction status. You can read more about statuses Statuses

“error_code” - error code; for a list of error codes, please refer to the page Error Codes

If you receive a message such as:

{
  "error_code": -1
}

Review the list of errors Error Codes