Thanks for the reply! Yeah I think my scenario is a bit more awkward than that. I'm wanting people who tipped previously to receive the newly dropped paid content for free. But as mentioned above, payments are stand-alone, so this wouldn't be possible from sound of things.
Viewing post in Question about tips and future DLC releases
Actually, your scenario is one of the rare cases where those individually priced file mechanics can be used. That pricing option is confusing and some use it to set a minimum price, and it has a lot of drawbacks, like if you change the price, you will lock out previous customers.
But if you give away the item for free and only want to give people that paid anything at all something extra, just upload files with an individual price of $ 1 and any such files will be accessible by all that tipped previously.
$ 1 is the minimum price that can be paid as far as I know. Maybe there are combinations with bundles that are handled differently, I do not know.
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Maybe I misread. If you made a new project that is paid and want to give that new project to previous tippers, you can either upload the files twice, once in the new project and as bonus files in the old project as described above.
Or more straightforward you can make a conditional sale of 100% with claiming enabled. Only those that "own" the required projects can purchase the sale according to the faq. "owning" means that someone paid something for a project or claimed it somehow. You can't claim an item by downloading it for free (excepting such an 100% sale with claiming enabled).
You might want to disable new purchases of the old project for the duration of the sale. Especially if the new project is priced higher than $ 1.
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Maybe do not overthink this too much, depending on how many people you want to reward. If we talk about 10 people that would be interested, you can just send them a download key for the new project manually.