I want to upgrade to the PRO plan, but the prompt states that my account uses advanced features that are not included in this plan, but I checked that the account meets the PRO plan requirements.
You checked this page? in the top of page should be listed your limits
Most usuall, at least the iussues that users faced here in community, is branches or managers. Pro plan doenst have much branches and have no manager at all, so maybe you need to delete yours before an upgrade. Check you resources (resources - managers)
Public or not, it doesn’t matter. From screenshot it’s visible that you have 1 manager + 1 in pending status, which means 2 in a summary.
Not sure about 3 file formats but should work anyway.
You need to delete manager from Project + delete manager(s) from the Resources (the page you see when you just log in into system, it’s near the glossary and translation engines and list of all your projects).