If you have a website that disallows the uploading of your app-ads.txt file at the root level (e.g., a site built and hosted by a site-generation service), you can use Firebase Hosting to host your app-ads.txt file.
Firebase offers a free, fast, and reliable way to host your app-ads.txt file with your own custom domain or on Firebase project's free subdomains: web.app and firebaseapp.com.
We have developed a step-by-step guide to help you set up and publish your app-ads.txt file with Firebase Hosting. Please refer to the developer guide here (Android | iOS) for more information.