https://www.pcgamer.com/deltarune-chapter-2-is-free-but-the-next-three-chapters-wont-be/
 
Deltarune Chapter 2 suddenly released last week, and contrary to what everyone expected it's free. The first chapter was free too, but this trailer is among several that forewarned that you'd need to pay to continue the story. That's pretty generous, but there's three more chapters coming in the future, writes creator Toby Fox, and those are gonna cost you.  
"Originally I had planned to release chapters only when all them are finished, but honestly, it's hard both for creators and fans to go a long time without a release. So, I changed my mind. I think most people will be happy about this," Fox wrote.
 
"My next goal is to complete Chapters 3, 4 and 5 for next time. Then, at that time I will ask for people to buy the game, at the price of the first 5 chapters (including 1 and 2). I don't know the price yet, but it's definitely going to cost more than Undertale." Elsewhere, Fox admits that he had intended to charge for Chapter 2 but that he decided not to since "the world has been really tough for everybody recently," likening himself to "a pet cat that drops bugs at your doorstep."
 
"Just one request," Fox adds. "Please remember, games like this aren't normally free. If you can afford it, spend the money you saved from getting this game for free by supporting other indie devs." It's been three years since the first Deltarune chapter released, and that can be attributed to a lot of development changes, including a new engine. If you're interested in Deltarune (or Undertale) it's well worth reading the post in full and, of course, playing the new episode.
 
Money doesn't grow on trees so charging for further chapters of the game is acceptable in my opinion.