Hook form alter not firing on a custom form that does exist
Before Drupal 8, the form ID is also the name of the PHP function that builds the form itself (or an ID contained in the array Drupal gets from a hook_forms() implementation).
As such, it can only contains those characters a PHP function name can contain. Underscores are allowed, but not so dashes; dashes are used in HTML. The correct form ID is the one with underscores.