When this error occurs, SendPro Online may also become unresponsive and you may be unable to edit the address or select the back arrow.
If SendPro Online is responsive, edit all lines in the sender and recipient addresses that exceed 23 characters so that they are 23 characters or less, including spaces. If the address cannot be abbreviated, another option is to separate the address to be on different lines.
If SendPro Online is unresponsive, you will need to close and relaunch SendPro Online. If you previously pasted the address in from another program, try typing the abbreviated address into SendPro Online instead of pasting.
UPDATED: 15 June 2021