passing validation error message in laravel 8 code example

Example: add error to laravel validation

//setup Validator and passing request data and rules
$validator = \Validator::make(request()->all(), [
    'due_date' => 'required',
    'template' => 'required'
]);

//hook to add additional rules by calling the ->after method
$validator->after(function ($validator) {
	
    if (request('event') == null) {
    	//add custom error to the Validator
        $validator->errors()->add('event', 'Please select an event');
    }

});

//run validation which will redirect on failure
$validator->validate();

//https://dcblog.dev/laravel-adding-custom-validation-errors