About acceleration and velocity

acceleration is a kind of vector which consists direction and magnitude

the reason why an object can be acceleraing when velocity is at rest is that the direction of the object is changed.
take throwing a ball from a lower position as an example.
when the ball reaches the maximum height, the velocity should be 0. however, there is still an acceleration which is used to change the direction of the ball. then the ball falls.

therefore, velocity is at zero does not mean that there is no acceleration.