Is the grandfather paradox theory really true for sending messages to the past or human time travel?

I am just curious about time machine theories because I was interested in what Ronald Mallet was saying on an interview. I searched youtube for the key word "time machine" and found out about him. His theory was to invent a time machine that would be turned on today and last for 100 years or more then he will expect to receive mesages from the future after he 1st turned on the time machine on day 1. He will then receive messages from day 10 or more from the future and reply. What if you send a message like the winning lottery numbers to the past so that you will win the lottery but it has no effect on the present at all. You just became a millionaire in the past dimension but in this present dimension you are still thesame. If the grandfather paradox is true then you should expect money to suddenly appear infront of you at present like magic if you sent a message in the past to win the lottery but what if sending messages to the past does not change anything in the present. But what if you can only send messages to the past to give warnings and change that dimenson in the past but here in the present you could not change anything at all like preventing murders, etc. Same for human time travel, if you kill your grandfather by travelling in the past then what if here in the present it has no effect at all? Maybe grandfather paradox is not true but you can just send text to the past or future normally like sending a normal text message? Meaning- no one can change the present?