Is it necessary to have a sim in my iPad to use iMessage ?

No if you are connected to wifi iMessage will work but if you are not connected to wifi it won't send, unless you have a sim card installed.

hope this helps! 😁

YOu should have apple id to send messages from imessage free with wifi

for creating appleid go https://appleid.apple.com/account

and if you also have apple id you should go to the setting,Messages,enable iMessage,enter your apple id and password.

it takes a several minutes to verify and after that you are able to start messaging with iMessage.

hope i help you