Even if a zip-file (the one provided from airship) is selected for upload, an error message tells no zip-file.

Please check because its a pretty much useful plugin regarding the opportunity to send push notifications with airship. It allows even semi technicians to use the solution.

Could it be a permission case while uploading the file?
Wordpress 5.2

The plugin is breaking the custom metabox order in wp-admin.

After activating this plugin, user is no longer able to have a custom order for metaboxes on the side of the post edit screen.

User can move meta boxes, but the order does not persist.

The bug is in the \UA_WEB_NOTIFICATION_ADMIN::reorder_meta_box method which is hooked to “get_user_option_meta-box-order_{$screen->id}”. Overriding user preference for the metabox order is not a good practice. It would be great if that filter can be removed.

Instead, the metabox could be added with a ‘high’ priority. Which is another bug in the plugin’s code:

add_meta_box(
	'webpushnotificationbox',
	esc_html__( 'Web Notifications', 'ua-web-notification' ),
	array( $this, 'render_notification_meta_box' ),
	null,
	'side',
	'core'
);

There is no priority called ‘core’. Possible values are ‘high’, ‘low’ or ‘default’. See: https://developer.www.ads-software.com/reference/functions/add_meta_box/