Yii2 active record model not saving data

Use

$prompt->save(false);

If that works that means that some validation rule fails.

Try

    if ($model->load(Yii::$app->request->post())) {
                if ($prompt = $model->post()) {
                    $model->save()
                    Yii::$app->getSession()->setFlash('success', 'Your prompt was created successfully!');
                    return $this->goHome();
                } else {
                    Yii::$app->getSession()->setFlash('error', 'Error while submitting your prompt.');
                }
            }

Okay, I figured it out. Turns out that if you declare public attributes in your ActiveRecord model, they obscure the automatic attributes that are created by AR. Data gets assigned to your obscuring attributes but doesn't get sent into the database.

The correct AR model should have been simply this:

<?php

namespace app\models;

use Yii;
use yii\db\ActiveRecord;

class Prompt extends ActiveRecord
{
    /**
     * @return string the name of the table associated with this ActiveRecord class.
     */
    public static function tableName()
    {
        return 'prompt';
    }
}