Lumen development problem: Call to undefined method Illuminate\Validation\Validator::make()

This error message is reported when doing form validation, because the Validator class is referenced incorrectly.

Incorrect:

use Illuminate\Validation\Validator;

correct:

use Illuminate\Support\Facades\Validator;

After switching the reference class, this error may still be reported

 A facade root has not been set.

To use the facade, it must be enabled manually, in bootstrap/app.php

Uncomment the line $app->withFacades();