SMS don’t show on iPad

This is the first thing I'd check too.

Maybe to clarify - this setting needs to be set on the iPhone that SMSs are being sent/received on, rather than the iPad itself.

If the iPad you're looking for is not listed under devices to forward text messages to, you need to check that both devices are signed into the same AppleID.

The setting has to be switched on on your iPhone. The iPad will only receive SMS/MMS messages forwarded from your phone. It will receive iMessages

On your iPhone, go to:

Settings > Messages

Select text message forwarding and toggle on the device (iPad)