If you receive an error message "Unable to execute because the shopping cart contains ongoing payments", it may be because you need to update the card terminal parameters. Remove the ongoing purchase, update the card terminal parameters and try again.
VX820
Log out of Sitoo POS to make the menu button on the terminal available: On the terminal press Menu > Express menu > Functions > Parameters
Bambora (Ingenico IPP350)
On the terminal press Menu (under the button 7) > Enter PIN 2020 > Settings > Update parameters
Nets (Ingenico IPP350)
Drag your Merchant card in the terminal > Card agreement (1) > Download card agreement (1) > [Wait] > GREEN button > GREEN button> [Wait] > RED button
Yomani
On the terminal press Meny > Enter PIN 123456 > Functions > Load parameters