How do I see a message on both my Iphone and iPad?

Be sure that you use the same Apple ID for both devices. When you do, you messages will be synced via your iCloud account that is associated with your Apple ID.

Ref:

• Use iMessage apps on your iPhone, iPad, and iPod touch - Apple Support
• How to Fix iMessage Not Syncing Between a Mac & iPhone/iPad - OSXDaily

Hi

Only iMessage will work on iPhone & ipad from other apple devices

Text message services are run by the network provider for mobile phones only.

Cheers

Brian 🇬-1F1E7;