If you have an iZettle account and card reader you can use iZettle to process your Shopwave card transactions.
To enable this in the Shopwave iPad app, go to Settings > Payments and select iZettle.
When you process a card transaction an iZettle window will appear, sign in the first time with your iZettle account. The payment amount from Shopwave will automatically be entered on the iZettle device.
For further help with iZettle visit https://www.izettle.com/gb/help