My first time clients can't get my promo code to work, what am I doing wrong?

Are they using both your personalized link and promo code? If yes and still it is not working, I would contact Rover support, they've always been very responsive and have fixed issues like this very quickly for me.

I just send a message to Rover telling them the client is having a problem using my code, and they credit the client as needed.

From my understanding, the promo code can only be used by customers that found you through your personal link and not on the Rover site.