If you have bought it in the past, you can still download a copy from the accounts tab in your App Store application. The product has last been tested on iOS 14. The Dropbox sync with the Mac app is probably going to stop working sometime in late 2021, because of changes in the Dropbox APIs.
I had a lot of big plans for Vitamin-R on the iPhone and the iPad. I spent a lot of time on version 1.0, but then reality bit: there is just no way of making enough money on a complex piece of niche software on Apple's iOS App Store.
While I was never going to be able to recoup the development cost, I continued maintaining the iPhone version as a service for the (handful of) people who had bought it already. Unfortunately, the rapid pace of breaking iOS updates, new screen resolutions, new technologies to adopt, new device models, etc. has meant that the cost of yearly maintenance was greater than the yearly revenue.
It is a shame for indie developer's such as myself, that Apple has chosen to embrace a race-to-the-bottom pricing model, scam-y subscription schemes, etc. instead of encouraging a healthy eco-system where developer's can directly interface with customers, offer free trials to convince users of the benefits of their apps and then rely on recurring upgrade revenue to continuously refine their apps.
What really killed Vitamin-R for iPhone in the end, was sync. It was the main reason for keeping it alive in the first place, but sync is hard.. really hard and very, very costly in effort and time.
I have never really had much reason to regret my choice of Dropbox sync for the Mac. It all just works with no embedded frameworks, no maintenance, login credentials, etc.
Unfortunately on iOS, Dropbox is not a great solution. It requires bundling the Dropbox framework, and Dropbox-the-company rather than Dropbox-the-technology is not a great partner.
They insisted on me using a higher-level framework to implement my file-based sync.. that took a huge amount of effort, but then it was done, and I was looking forward to spending more time on adding user-facing features.. but soon Dropbox decided that the higher level framework that they had insisted on just months ago, was a dead end, and they dropped it, and compatibility with it, with very little notice, forcing me into a fast and complete rewrite of the most complex part of the iOS app.
I would estimate that both sync implementations took around 50% of the entire product development effort; and that translated into most of the available development time going into just keeping sync working.
Just today, they have announced that I'd need to do a further migration, because they are deprecating the connection model that my app relies on.
I had started a re-implementation of Vitamin-R for the iPhone using the SwiftUI frameworks, despite there being no prospect of that effort ever resulting in more favourable economics. I justified it as a learning experience.
Unfortunately version 2 is still a long way from being ready to ship & the Dropbox changes are going to hit way too soon. I'm afraid that spending a significant amount of time on the now pretty much defunct v1 code base, only to then redo the same work on the v2 code base, just so that I can keep a product that I'm not happy with and makes no money the App Store, would just be crazy.
So, today with a heavy heart, I have come to the conclusion that my efforts are better spent on Vitamin-R for the Mac, my other apps & new product ideas.
The good news is that Vitamin-R for the Mac is still very much alive and kicking & at the time of writing, a brand-new Version 4 is about to go into beta.
I'm sorry for any inconvenience caused.
Thank you for your comprehension.