This is an important unresolved issue with the latest App Bridge and Polaris we’re supposed to be using now. There seems to be no documentation or clear way in plain vanilla JS to tell the automatic saveBar (the one that shows with a <form data-save-bar>) that the form submission wasn’t successful and the saveBar shouldn’t get dismissed. Even worse, there is no way currently to actually instantiate a saveBar manually. As the other post explains, there is some ID missing which doesn’t exist and can’t be specified. SaveBar API mismatch between docs and real code?