Embed accepts an onEvent parameter that can be used to listen to certain events emitted from the form. 
setup({
  element: '.container',
  ...,
  onEvent: (name, data) => {
    ...
  }
})
Embed emits the following events:

​
argumentError

Returned when the initial input (element, options) are incorrectly formatted or missing. 
{
  "code": "argumentError",
  "option": "currency",
  "message": "must be a valid number"
}

​
optionsLoaded

Returned when options are loaded. Stored options include the id. 
[
  {
    "id": "...",
    "method": "card",
    "mode": "card"
  },
  {
    "method": "card",
    "mode": "card"
  }
]

​
formUpdate

Returned when the form updates. Currently this only informs the developer if the form is valid. 
{
  "valid": false
}

​
transactionCreated

Returns a full transaction object when we accept the transaction, regardless of its status. Be aware that this can be a pending or declined transaction. To track API failures please use the transactionFailed event. 
{
  "type": "transaction",
  "id": "8724fd24-5489-4a5d-90fd-0604df7d3b83",
  "status": "pending",
  ...
}

​
transactionCancelled

Returned when a buyer has explicitly canceled a transaction, e.g. closing a popup or dismissing Apple Pay. This is currently not supported for 3-D Secure transactions and should not be conflated with transaction being declined or an error occurring. 
{
  "type": "transactionCancelled"
}

​
transactionFailed

Returned when an API call fails to create a transaction due to a client or server error. In other words, this event is raised when incorrect data (like an invalid JWT) is passed to our API and a HTTP status code in the 4XX or 5XX range is returned. To catch failed or declined transactions due to downstream issues with the payment service, please subscribe to the transactionCreated event. 
{
  "type": "error",
  "code": "unauthorized",
  "status": 401,
  "message": "No valid API authentication found"
}

​
apiError

Returned when the form encounters an API error. 
{
  "type": "error",
  "code": "unauthorized",
  "status": 401,
  "message": "No valid API authentication found",
  "details": []
}

​
cardDetailsChanged

Returned when the card BIN changes in the form. It contains information on the inputted card, such as the BIN, card type and scheme. 
{
  "bin": "42424242",
  "scheme": "visa",
  "cardType": "debit"
}