So, a neat trick I discovered recently in Pokémon Ultra Moon is a method of making money. I was selling things to get enough money for the Luran set, which is a set that is themed like a Lurantis and it's honestly really cool looking.

For this method, you're gonna have to do a lot of Mantine Surfing, unless you only need a little bit of money. This will get you Beach Points, or BP for short. Now, since I personally enjoy Mantine Surfing, this wasn't even a problem for me. I was able to do it for quite a while without getting bored.

When you've gotten a lot of BP, head to the person who sells you useful items for BP. It should look like this:

Now, what you're gonna need for this method is Carbos. These only cost 2 BP and sell for 5,000 Pokédollars each.

Buy a lot of Carbos and sell them at the Pokémon Center. Then you'll have a lot of money!