Is the payment to RetargetApp connected to my other payments to Facebook or Shopify?

No. For security reasons RetargetApp doesn’t access the payment methods which you have connected to your Shopify account or Facebook Ads Manager/ Business Manager.

This means that you have to input the payment card details into the app during the initial campaign setup. This also means that, if you find it more convenient, you can use different cards for RetargetApp, Shopify and Facebook.