Hello pei-pei139,
Thanks for reaching out to us with this issue you're having with the headphone buttons not working on your iPad. We'd like to gather some more info, so we will better know how to assist you with this. Does the iPad recognize that the headphones are connected? Do you hear any audio at all using the headphones with the iPad? If you are experiencing any of these issues, get some steps to fix your trouble here:
If your headphones don't work with your iPhone, iPad, or iPod touch
If your trouble persists, get in touch with Apple Support for further assistance:
Get Support
We hope this helps you.
Have a great day!