Only transactions in the "Submitted" status can be canceled, but that is dependent on the amount of processing that Veem has completed. If it's a large amount, Veem may have already started processing some of the payment.
To check the status of your payment, see the help article on how to check the status of my payments/invoices.
From your Dashboard or Transactions tab, locate the transaction you want to cancel. Hover over the transaction to reveal the blue arrow to the right. Hover over the blue arrow click the 3 dots and click "Cancel Transaction".
Note: If you are able to cancel the payment, you will see the "Cancel Transaction" option. If you do not see that, then you will not be able to cancel the payment online. You will have to contact our Customer Success team to assist in canceling the payment. Note that it may be too late to stop the processing.
Click "Yes" to confirm the cancellation. 
That's it! You will be returned to your dashboard and will receive a popup notification advising that the payment was canceled. You will also see the payment status change to "Closed" in your Transactions view.
Still need help? You can chat or call our Customer Success team here.