Unable to connect webcam on iPad Pro

Is it an external webcam, or are you talking about the front camera of your iPad?

Should be the former, contact that webcam manufacturer support team and ask them.

Should be the latter, if you're sure that nothing (case/cover, screen protector, dirt) interferes with your front camera (remove any obstacles, if present), I suggest that you put your device on charge for at least half an hour, then, keeping it plugged in, try a "forced" restart of your iPad, using these instructions:

• On an iPad with a Home button: Press and hold the power button and the Home button at the same time. When the Apple logo appears, release both buttons.
• On other iPad models: In rapid sequence, press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the power button. Only when the Apple logo appears (it might take 10-20 seconds), release that button (ignore all other screens that might appear, the one with the "slider" to turn the device off included).

If the issue still persists, contact Apple Support, using this link:--> Contact Apple for support and service

Regards

Giulio