See also the Transaction response object.

This functionality is specific to Braintree Marketplace merchants.

$result = $gateway->transaction()->holdInEscrow('transaction_id');

If the transaction can't be found, you'll receive a Braintree\Exception\NotFound exception.

You can only hold a transaction in escrow if its status is authorized or submittedForSettlement.

transactionId required, string

The id of the transaction you want to hold in escrow.