My iOS trial has expired but I can't purchase a direct subscription

I was previously using the Dropbox Plus plan, but after it expired, I started a free trial through the App Store. Now, I've canceled that trial and want to purchase the plan directly using my credit card, but I don't see an option to do this on the Dropbox website. I also prefer not to make the purchase through the App Store again. Unfortunately, I haven't been able to get any support from Dropbox on this issue. If anyone knows a solution, I’d really appreciate the help.