You pretty much answered your own question, minus the fact that you obviously haven’t properly searched for how to do this. A five second search revealed a support topic about stage skipping with given code and fixes to the problem.
Its not just the DevForum that you should search before giving up and resolving to post a thread. Check the toolbox, check online, there are definitely resources you can use to help you accomplish your goals.
You want to create a script that skips a stage if you buy a product. Great. Figure out your needs first.
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Do users need to buy the product? Obviously. PromptProductPurchase.
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Do you need to do something when players buy the product? Yes. ProcessReceipt.
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What do you need to happen when the player buys a product? Skip a stage. Increment their stage value and teleport them to the next stage.
There you go. Go try stuff out. This category isn’t a place for you to receive code. If you don’t know how to, try it first at the very least. Category guidelines, for reference.