You can do whichever. Some people only have a teaser or just a few chapters and then say you have to buy the book to read the rest. Others will have the less…published? version on wattpad with the fully edited and polished version for sale. This allows for the full book to stay on wattpad but it’s not the exact same as the published version.
Example: The Cell Phone Swap. The wattpad book is called The Cell Phone Swap. The published version for sale is the same book but now titled Textrovert and it’s got some changes in the book that make it different from the wattpad version so that the published version isn’t the exact same. This just allows people to keep full books on wattpad but still have some kind of leverage for the published version to sell, as they mention the changes.
I plan to self publish and this is the route I wanna take. I want to keep the full book on wattpad but I will have the published version be fully polished and edited and it will be a bit different and not an exact copy of the wattpad version.