Media Matters created accounts and then exclusively followed accounts that posted white nationalist/antisemitic/racist content as well as big corporations that post paid adverts. They then began refreshing their timelines until racist content appeared alongside these paid ads. They took screen shots and went to the corps basically saying 'is this what you want your company/brand/product to be associated with?' and obviously lots of them all said no way and pulled all of their adverts from X threatening a huge loss in revenue for Musk's company.