iMessage
Get messages on my IPhone but not on my IPAD
Question marked as
To use SMS/MMS messaging from the iPad Messages App, your iPhone must be logged-in to iCloud with the same AppleID - and message forwarding to your iPad must be enabled on the iPhone.
https://support.apple.com/en-gb/HT208386
I hope this is helpful in clarifying your iPads Messaging features - and in resolving the problem.