So, I have a zine project that is selling both SFW and NSFW content. We have a community copies program to allow people who can't afford the zine normally to be able to get the zine. The community copy program only allows access to the SFW zine bc it was important to me that NSFW content be sort of locked behind needing either a credit card or paypal account, to prevent minors from just using the community copies to get access to free NSFW content. 

The problem is that there are actual adults who could benefit from the CC program and might want to upgrade to the NSFW version of the zine. Initially I assumed it would be easy enough for them to just select the CC reward (which is set to $0.00) and add a $5 donation (thus proving they're an adult bc they'd need a credit card to send that money) and then we would send keys them that would get them the NSFW zine. However when ppl try to donate on a $0.00 CC, the project doesn't let them bc it wants them to pay the normal minimum for the project of $15. 

Is there any way to solve this? I don't want to remodel our entire set-up for this fringe case, since I expect low numbers, and PWWYW model would otherwise likely confuse the crowd of people we are selling to, since zines in this fandom are not usually sold on itch.

Add the demo project in twice. 

Select the option for the first one: this is a demo can be downloaded for free. 

Then for the second one set the price to $5.

Then people can choose to get the demo for free, or pay $5 for it - in which case you would have to manually send them a download key for the full price project. However, if you're going to do that, you may as well just change the price to $5 because everyone will most likely choose that option and you're creating extra work for yourself.