Hi kenishaclarke-li,

Welcome to Community!  QuickBooks Online Payments Canada, currently does not accept AMEX as a payment option for your customers.  To learn more about the accepted payment methods click here.  If this is something you would like to see available in future updates, please don't hesitate to submit a suggestion to our Development Team.  In the meantime, as mentioned by 4Gal, you can review available options for a third party app that integrates with QuickBooks Online.

If you have any other questions, feel free to touch base again.  We would be happy to help!