Why can I not receive text messages on my iPad that show up on my iPhone
Why can I not receive text messages on my iPad that show up on my iPhone. It used to. But it isn't anymore. It is rather old. I think it's a at least 10 years old
You must explicitly enable Text Message Forwarding for your iPad on your iPhone.
On your iPhone:
Settings > Messages > Text Message Forwarding - set to ON - and explicitly enable your iPad from the list of devices.
You might also be best advised to ensure that Messages in iCloud is enabled on both your iPhone and iPad:
Settings > [Your Name / AppleID] > Messages - set to ON
More information:
Fault finding if needed:
If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support