Flutter "flutter build web" Fails in CI

A Flutter web build failed. Either web support is not enabled on the runner, a plugin in the dependency tree has no web implementation, or a renderer/wasm flag conflicts with the project.

What this error means

flutter build web exits non-zero - either "Web is not enabled", a missing web implementation for a plugin, or a compile error specific to the web target. The mobile build of the same app may pass fine.

Flutter output

Building a web application requires the Flutter Web feature to be enabled, ...
# or
The plugin `native_only_plugin` requires your app to be migrated; it has no web implementation.

Common causes

Web support not enabled on the runner

On a runner where web is not configured, flutter build web refuses to run until the web feature is enabled.

A plugin without web support

A dependency that only implements Android/iOS has no web platform code, so the web build cannot resolve its platform interface.

How to fix it

Enable web and confirm devices

Turn on web support before building.

Terminal

flutter config --enable-web
flutter devices
flutter build web --release

Guard or replace native-only plugins

Identify the plugin with no web implementation from the error.
Replace it with a web-capable alternative, or guard its use behind kIsWeb.
Pick a renderer explicitly (--web-renderer canvaskit|html) if the failure is renderer-specific.

How to prevent it

Enable web support as an explicit CI step before building.
Check plugin web support before adding native-only dependencies.
Test the web target in CI if you ship a web build.