how to use cellular data for imessage on ipad?

KRISTINE1899 wrote:

I CAN'T SET UP IMESSAGE WITH MY NUMBER, ONLY HAVE ID SUPPORT AND NOTHING MORE.

That is correct. The "mobile number" on an iPad is for billing purposes only. It can't be used by the end user to send or receive calls or messages. On an iPad, you can only set up iMessage and FaceTime with your Apple ID.

If you have an iPhone, you can connect the iPad to that to send and receive messages using the iPhone's number.

Forward SMS/MMS text messages from your iPhone to your Mac or iPad - Apple Support

One request: please don't type all in capitals. It's very hard to read and, according to internet etiquette, is considered shouting. Many people won't even bother with a post typed all in caps.

What model iPads do you have? If you have the cellular capable iPads, have you set up service with your carrier? What happens when you turn off WiFi and try to send a message?