Not all clients like to pay through Trainerize pay, but are happy to pay via cash and card reader payments instead.

Zettle offers these options, but must track product sales separately. It would be great to have the option to sell products listed on Trainerize pay (e.g. 2 per week 1-2-1) via both the current Trainerize Pay system and Zettle integration in order to track sales more easily and consistently.

I would suggest this is done via mobile for simplicity of inter-app communication. This could either be a separate Trainerize Pay App which either integrates Zettle into the Trainerize Pay app, or opens up in the Zettle app, to take the payment.