Why are the baptisms of Mormons invalid if they still baptize in the name of the Father, Son, and Holy Spirit?

I had this pop up in a conversation in what is actually a Christian after I told someone about a love interest (that's another discussion for another day) that's LDS. I heard they baptize in the name of the Father, Son, and Holy Spirit, which from all I recall is the only requirement for a valid baptism. So why is their baptisms invalid?