having trouble syncing new ipad with my iphone

First, ensure that your iPad and iPhone are signed in to the same apple ID by opening settings on both devices; you should see your name at the top of the first page of settings. Click your name on the next page you should have a summary with your profile picture, name, and the email address that you use as your Apple ID.

If both devices are signed into the same apple ID go to Settings > Messages > ensure that iMessage is turned on for both devices. click send & receive, and ensure both devices are signed into iMessage and have the same accounts selected.

Then to forward all text messages go to Settings > Messages > Text Message Forwarding > you should see a list of all devices signed into the Apple ID that you can forward to. Turn on the switch next to your iPad.

How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

You can use iCloud for Messages on both devices and the Messages app will sync all messages. You have to ensure that both devices are using the same Apple ID and Text Message Forwarding is setup on your iPhone.

On both devices, open Settings ➡️ Apple ID (Your Name at Top) ➡️ iCloud ➡️ Messages: Set this switch to ON.

On your iPhone, open Settings ➡️ Messages ➡️ Text Message Forwarding: Set this switch to ON for your iPad.

Axel F.