Hey there.
I recently completed an Apple Pay (on the web) integration and it has been working fine, for the most part. I had one customer contact us saying that it didn't work on his devices though. I checked it out, and while it does normally work (and we've had over a thousand transactions use it) there does seem to be some scenarios where it fails and I'm not sure why.
I was able to replicate his issue (or at least an issue) by using BrowserStack. When I click the button which should initiate the payment, everything works in the JS code until it gets to the applePaySession.begin() function call. Once it hits that, it just stops. No errors are generated and no notice is given that anything is wrong until you try to do it a second time. Then an error about a payment session already being active on the page is thrown.
I'm not really sure how to troubleshoot this since I know it works on my old iPad Air 2, my current M4 Macbook, multiple other devices, and also works when scanning the QR code for use on an iPhone.
There is some very specific thing with some very specific versions of Safari that seem to be tripping it up.
If it helps, the version of Safari on the BrowserStack device is 18.1, but the version on my Macbook is 18.1.1. The version the customer who is having the issue is on is 18.2 according to him.
The customer also says they have used ApplePay on other websites with no issues. I checked one of them and they appear to be using a PayPal integration, where as I am using the ApplePay SDK straight from Apple.
There are quite a few variables at play here, and I'm just trying to narrow down what I should be looking at. If one person is reporting the issue, there are probably others with it as well.