It turns the I needed to follow the format outlined here: https://developer.apple.com/library/archive/documentation/General/Conceptual/AppSearch/UniversalLinks.html{
"applinks": {
"apps": [],
"details": [{
"appID": "12345NGB.co.uk.my.app",
"paths": ["/universallink/*"]
}]
}
}The Apple documentation is very misleading because it suggests that's an old format for supporting iOS 12 and earlier.