Cannot add posters

I am trying to add/change posters for my titles. When added they don’t show up in the list of available posters.

I am using Plex on chrome (Mac)

The Local Media Assets agent must be active.
After adding a poster file you must at least update the library.
You must make sure that the filenames of your posters are one of the supported variants.
https://support.plex.tv/hc/en-us/articles/200220677-Local-Media-Assets-Movies