App Transport Security blocks routing via custom url scheme

Question

My iOS app (written in Swift and React Native) has a custom url scheme that allows me to route to the app from e.g. Safari like this myappscheme://https://www.mywebsite.com/somematerial. If I enable App Transport Security in my app, the routing via custom url scheme is blocked and I get this message:

App Transport Security has blocked a cleartext HTTP (http://) resource load since it is insecure. Temporary exceptions can be configured via your app's Info.plist file.

However, if I disable ATS, the app routes as expected. I am not accessing any link via http in my app and in my routing I always fetch data via https. Therefore, I don't know why ATS is blocking this routing. Do you know if I have to provide some additional info about my url scheme?

Please see my ATS configurations in Info.plist:

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSAllowsArbitraryLoadsInWebContent</key>
    <true/>
    <key>NSExceptionDomains</key>
    <dict>
        <key>localhost</key>
        <dict>
            <key>NSIncludesSubdomains</key>
            <true/>
            <key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key>
            <true/>
        </dict>
    </dict>
</dict>

I've also whitelisted my custom url scheme:

<key>LSApplicationQueriesSchemes</key>
<array>
    <string>myappscheme</string>
</array>

Answer 1

This issue has been resolved. I logged out the endpoint I was hitting and checked if it satisfied ATS requirements by doing in Terminal:

nscurl --ats-diagnostics https://www.example.com/

It turned out that the particular subdomain I was trying to fetch failed all ATS requirements. My server team has fixed the issue and made the endpoint secure.