You can now return an
action along with your
card-back-section in order to show a button at the top right of your section.
action consists of two required properties:
text - The text to show on the button
callback - The function to be called when the user clicks the button
Your callback can do anything a
card-button callback can do, such as opening a
t.popup or a
t.modal for example.
Check out the full docs for the
card-back-section capability for more information: https://developer.atlassian.com/cloud/trello/power-ups/capabilities/card-back-section/