Your first bounce is too close to the net which makes the ball can’t get over. Try to adjust the placement nearer to your body and lower the contact point of racket and ball to keep it short and low.
Answer for How to correct my backspin serve
Your first bounce is too close to the net which makes the ball can’t get over. Try to adjust the placement nearer to your body and lower the contact point of racket and ball to keep it short and low.