What did he do wrong?
Roses are a euphemism for payments rendered to a sex worker. Typically, trans women will pretend to be interested in a relationship, but this is just a pretext for getting past a gullible loser moid's trust issues. Once trust has been established, perhaps a few months later, the subject of payment is raised. In the painting, the negotiations did not go well, and she is chastising him for "thinking it was free". By ensuring that freeloaders like him are appropriately stigmatized, she is protecting her market value. She just wants someone who wuuuuvs her for who she is uwu.