In this video <https://youtu.be/2o3-GTk72x8>, Professor Michel Biezen derives the following equation :

$$mx’’+m\ell \left(\theta’’ \cos(\theta)-\sin(\theta)(\theta’)^2\right) = -kx. $$

However, the terms inside the bracket are not dimensionally equal (the coefficient of $\sin(\theta)$ is not dimensionally equal to Force), so there must be some error in this equation. I cannot figure out exactly where the error as but my best guess is the error comes in after applying the product rule right before this equation is written at 3:47