280k is not a high number for a senior SAP consultant with a big mouth, but 4M indeed is but definitely not impossible or even rare. Anecdotal, but at least I already know 1 person from my own friend group, a friend worked as SAP consultant in utility; he started his own company specializing in SAP for utility but he wrote specific small tools for parts where SAP was(is?) very hard / cumbersome to use or where it has gaps for the particular (big) electricity providers he contracted for. Selling those on the side next to his high contracting fee, he made (makes) millions.