Sms problem

ipads can't send sms on their own at all

to do so it require an iphone with the same appleID

read

How to get SMS text messages on your iPad | iMore

the same holds true for mac computers

if you just CANNOT send sms then check that you are using an activated SIM card.

Go to messages settings in the settings app and turn off iMessage. You will know it has worked as it will ONLY send green bubbles not blue