onPaid listener not firing in popup.js

[FlashInThePan]

I have put the following in my manifest.js

{
"content_scripts": [
{
"matches": ["https://extensionpay.com/*"],
"js": ["ExtPay.js"],
"run_at": "document_start"
}
]
}

and the following in my popup.js:

extpay.onPaid.addListener(user => {
console.log('user paid!')
})
(I noticed that this block is commented out in the V3 sample extension).

Unfortunately, the event listener isn't firing when subscription paid.

Any advice appreciated.

[Glench]

I would recommend putting onPaid listeners in the background file, not the popup because the popup often closes when the payment popup is opened.