Powerup required security settings
Because of the way Trello embedded powerups like Amazing Fields using iframes, Trello powerups require third-party cookies to be enabled for *.trello.com sites. This allows the powerup and the Trello powerup libraries to store settings in your browser's localstorage.
Trello has an article about this: Trello support: Enabling localStorage
Amazing Fields Warning Message
I try to have Amazing Fields detect when this setting is missing and present users with a clear dialog about how to handle it. The dialog looks similar to this:
To enable Trello to store powerup settings in Chrome, to go chrome://settings/cookies
Firefox and Edge
Follow the instructions from Trello here: Trello support: Enabling localStorage