How long after a rejection can you reapply?

I’m an international student doing my uni in London. I applied for a Schengen in dec end from Finland and got rejected on the basis of “we couldn’t justify the reason and terms of your stay” I spoke to a couple agents and they said a rejection is inconsequential but I really wanna understand facts before I go ahead with applying again as I don’t wanna get banned if I get rejected again. Planning a Spain trip next month so thinking from applying there. Any guidance is appreciated :)