If you updated the android SDK, the licenses may have changed. Depending on how you did the update you may or may not have been prompted to accept the changes, or maybe it just doesn't save the fact that you did accept them in a way flutter can understand.
To resolve, try running
flutter doctor --android-licenses
This should prompt you to accept licenses.

If you updated the android SDK, the licenses may have changed. Depending on how you did the update you may or may not have been prompted to accept the changes, or maybe it just doesn't save the fact that you did accept them in a way flutter can understand.
To resolve, try running
flutter doctor --android-licenses

This should prompt you to accept licenses (it may ask you first, in case just type `y` and press enter - although it should tell you that).
If you still have problems after doing that, it might be worth either opening a new bug in the [Flutter Github repository][1], or adding a comment on an existing issue like [this one][2] as it may be what you're seeing.

[1]: https://github.com/flutter/flutter [2]: https://github.com/flutter/flutter/issues/16025