Honest to god, I don't know why I'm going to give this full write up, but here goes nothing.
Everyone's labor, art or otherwise, is a transaction. If you want a webtoon of your novel, then you need some way to pay for it. Generally that means money, but sometimes exposure or fame is traded, though that is rare.
Almost all transactions are going to be monetary, any that aren't are most likely scams, though there are situations were "exposure" is valuated at a monetary amount and factored into a contract.
As an example of this that should be easy for you to understand: If a popular webtoon animator came to you and said, "I'd like to make a webtoon of your story, you'll be paid in exposure." You'd likely accept. They hold the audience, and you want access to the audience.
If you flip your roles though, you don't have an audience to offer, instead you would have to buy BOTH the artist's labor AND pay for access to their audience. This would be very expensive.
There are things you can negotiate for. As an example, if your story had a reach of say, 20k readers across multiple websites, you could maybe negotiate that you'd pay for them to make a pilot episode, and if it did well, you would pay significantly less for future episodes and they would keep the profit.
TL:DR You've asked for voluntary slave labor breaking rocks. Ain't no one gonna do that.