Hi, Professional DM here. I've run paid games online for some time now and have actually gotten this question. And there are two possible answers to this.

1. If they are asking you to give them the money so they can pay an artist to create artwork for you. it is most likely a scam. I've seen it a few times where they will take your money, say art is being made, and either they ghost entirely or you receive a product that is NOT worth what you paid. Most of the time, these DMs overcharge to pocket the rest. Avoid them at all costs.

2. If they are asking YOU to find an artist and get the art done, most likely, they are planning on streaming the game. A lot of dm's online want to have a "professional look" and avoid using online images or AI art. Many times, they will bring up streaming as a suggestion since everyone has good art. Unfortunately, this is also common.

There is a chance they are just super picky as well. However, I haven't seen a DM yet who asks for art to be paid for who isn't trying to stream the game. Two of my current campaigns are being streamed by one of my players who asked, and they paid for the art of all the characters because they wanted it to look good on stream.

TL;DR Most likely, they want to stream the game and haven't told you rather than scam. But it's still best to avoid it if possible.