"“A lot of people are turned off by the phrase ‘flat earth’ ... but there’s no way u can see all the evidence and not know ... grow up,” he previously tweeted, and then deleted.
B.o.B claimed that if the Earth was indeed curved, we would see that curve on the horizon.
“The cities in the background are approx. 16 miles apart ... where is the curve? please explain this,” he posted in another tweet in January 2016."
https://www.news.com.au/technology/science/space/elon-musk-shuts-down-flat-earth-conspiracy-as-social-media-brags/news-story/4516c2b931006a4613d69aca8ed31daa
"The Flat Earth Society replied assertively to Musk.
Hi Elon, thanks for the question. Unlike the Earth, Mars has been observed to be round.
We hope you have a fantastic day!"
https://www.cnet.com/science/flat-earthers-to-elon-musk-mars-is-round-silly/
Elon Musk humiliated the Flat Earth Society with a simple question
https://www.thesouthafrican.com/lifestyle/elon-musk-vs-the-flat-earth-society-the-battle-weve-all-been-waiting-for/