Volunteer Here!
Please follow this guide closely, it's there for a reason because it works, I followed this same guide long ago and have ranks working fine to this day.
https://itemsadder.devs.beer/plugin-usage/adding-content/ranks-textures-prefix
If you have any question specifically about the process, I can help, otherwise there is no telling where you might've went wrong.
For troubleshooting tips, its always helpful to check console and client log.
https://itemsadder.devs.beer/faq/identify-why-textures-are-not-shown
