Choosing between the two comes down to your requirements. If you want your app to have a real-time database, you should go with Firebase . If you require more efficient queries during development, you should pick REST APIs. You can also combine the two by having a Firebase database attached to your REST API.
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The Backendless SDK for Flutter provides backend support for Flutter web applications as well as Android and iOS mobile apps . Now, your Flutter app can enjoy all the functions and features of a Backendless backend on both web and mobile.30 Kas 2021
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Here are some great backend options for the Flutter app.
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