Installation for iOS devices uses Apple's Shortcuts app and Safari.
It might seem like a lot of steps, but they are just very detailed (helpful for the least computer savvy users).
If you just signed up for a new account and started a free trial, the page will refresh, and Closet Tools will disappear. Don't worry, just open it in the share menu again (step 17) and it will pop up.
You’ll want to set your screen so it doesn’t turn off. That way it always stays open and awake. If you don’t do this, the assistant will stop because it can't run in the background on iPhones/iPads.
To do that, open the Settings app. Open the Display & Brightness menu. Select the Auto-Lock option. Select the Never option.
You need to launch Closet Tools using the share menu (step 17) each time you want to use it after refreshing the page or navigating to another page in Poshmark.
You can check out all of the features of Closet Tools and how to use them over on the documentation page.