Zend certified PHP/Magento developer

Applepay Magento Flutter

We have integrated ApplePay on our Flutter App which is using Magento RestAPIs. We need to deactivate OR Pause OR restrict user to addToCart when redirected to Applepay because in Magento user may be access the account using other device and the flow of Applepay is to pay first then checkout. Now we are having concern if any user navigated to payment and from other account he’s added another product to the cart that particular amount is not sent to applePay.
Need assistance in this regards.