"What ingredients do you need?"

Translation: 무슨 재료를 필요로 합니까?

[raemation]

Can someone explain this sentence please? Why do we need 로?

[josueetcom]

A가 필요하다 means "A is needed" or "(I/topic) need A" but since the subject particle is used it reads more like "(Regarding me/topic), A is needed".

A를 필요로 하다 also means "(I/topic) need A" but reads more like "(I/topic) do need A".

The nuance is a bit hard to explain since -로 indicates a means of doing something but the main thing to keep in mind is that the two are equivalent but you need to use the subject particle -이/가 with 필요하다 and object particle -을/를 with 필요로 하다

[n.aandeg]

I don't think 필요로 하다 is correct here. 필요하다 and 필요하다 have a different nuance. 'To need' and 'to make into a need.'