Login with facebook shows error as unsupported request and failed to login

I'm not exactly sure about your situation but I came across this error message myself in the last few days after updating my Facebook SDK.

After reading through some documentation I found this page... https://developers.facebook.com/docs/facebook-login/android/deprecating-webviews which talked about web views being deprecated and to ensure that custom tabs were setup correctly, which in turn lead me here... https://developer.chrome.com/docs/android/custom-tabs/

I found that Facebook SDK 12.1 required that I set androidx.browser:browser to 1.3.0 or higher to function properly with custom tabs.

This required me to then increase my minSdkVersion to 24 which I didn't want to do.

So after a bit more experimenting I found that I could go back to Facebook SDK 8.2, which still functioned fine in my case, and continue using an older version of androidx.browser:browser allowing me to keep the lower minSdkVersion.

Hopefully that helps you too.

Edit: Just for completeness, what I am currently using in my dependencies is...

implementation 'com.facebook.android:facebook-login:8.2.0'
implementation 'androidx.browser:browser:1.0.0'

and to get Facebook login 12.1 working I had to use...

implementation 'com.facebook.android:facebook-login:12.1.0'
implementation 'androidx.browser:browser:1.3.0'