Hi Usertkn,
Welcome to Apple Support Communities. First, make sure that you are signed in with the same Apple ID on both your iPad and iPhone.
“1. Open the Settings app.
2. Tap Sign in to your [device].
3. Enter your Apple ID and password.
4. If prompted, enter the six-digit verification code sent to your trusted device or phone number and complete sign in.”
Above steps and other guidance can be found in Sign in with your Apple ID.
Does this happen only with text or iMessage as well? If only with text, make sure that SMS/MMS forwarding is enabled.
"1. On your iPhone, iPad, or iPod touch, go to Settings > Messages > Send & Receive. On your Mac, open Messages, choose Messages > Preferences, then click iMessage. Make sure that you're signed in to iMessage with the same Apple ID on all your devices.
2.On your iPhone, go to Settings > Messages > Text Message Forwarding.
3.Choose which devices can send and receive text messages from your iPhone. If you're not using two-factor authentication for your Apple ID, a verification code appears on each of your other devices: enter that code on your iPhone."
Check out How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac
Also, make sure that your message notifications are set up correctly from Settings > Notifications > Messages on both your iPhone and iPad. Reference Change message notifications on iPhone if needed.
Have a great day!