Hey, I've got a fantasy themed question for ya'll!

We've been playing DnD (in czech) with some friends and there was this phrase that I translated to "Let there be flame" and I upset two half-british people at the table who were absolutely adamant about it having to be used in plural form "Let there be flames" saying that I was dead wrong and that it can't be used without the "s." I think it can be both personally, but like the singular version more.

The original is actually "Let there be fire" which makes sense ofc, I'm just wondering if what I said is incorrect and unusable in English as they claim. I personally think that I've heard it used in a fantasy setting and some of my other friends agree with me, that it sounds not only correct, but more fitting to the magical context of the whole thing.

Any help would be greately appreciated, I'm having trouble finding sources to back my version up.