If for any reason your connection to the service is lost, for example if your Internet connection is interrupted while you are in the middle of a payment transaction, you can check whether or not the particular payment has been submitted by referring to your Payments history (Payments > History)
If you can see it in the history, this means it has been made successfully and you can print or save the transaction copy.
If you cannot see it in the history, this means you will have to repeat it.