According to the documentation for remove_action() the function name and priority must match the usage where the function was hooked. You have made a common sense assumption that a higher priority should be used for the removal but I believe that is the cause of the problem.
Docs:
https://developer.wordpress.org/reference/functions/remove_action/
To remove a hook, the $function_to_remove and $priority arguments must match when the hook was added. This goes for both filters and actions. No warning will be given on removal failure.
Update your remove action statement to explicitly define a priority of 10:
remove_action( 'wp_footer', array('External_Plugin','inject-code', 10 ) );
Related Posts:
- post formats – how to switch meta boxes when changing format?
- Content hooks vs User hooks
- Restrict post edit/delete based on user ID and custom field
- Adding an assisting editor box to Post page
- Get updated post meta on save_post action?
- Metabox Data not being saved [closed]
- Post IDs missing on delete_postmeta action hook
- Options to get my custom post type metadata via the WordPress API
- Set default Custom Post Meta Value
- How to prevent further updates of custom meta when using actions to set one meta based on another
- Add box with custom per-page properties
- wordpress is_front_page() issue
- add post meta front end edit
- I can not display meta value in extras.php and template-tags.php
- Add post meta data date to event
- Check if any meta on the post has value then display content
- Get or set values in post meta
- I created a Custom Meta Box but it is not displaying the value on my post page
- update_post_meta() throws Uncaught error: Cannot create duplicate attribute
- How to call get_post()?
- How we insert values into database using metabox WordPress?
- Post meta box data not saving
- Filtering Tabs in a Custom Post Type’s Edit Page
- Hide individual page title using checkbox in custom meta box?
- How do I retrieve the slug of the current page?
- Most efficient way to get posts with postmeta
- Get posts by meta value
- Explanation of update_post_(meta/term)_cache
- How to extract data from a post meta serialized array?
- Passing error/warning messages from a meta box to “admin_notices”
- Add “upload media” button in meta box field
- How to save an array with one metakey in postmeta?
- WordPress is stripping escape backslashes from JSON strings in post_meta
- How can I get the post ID from a WP_Query loop?
- Check if Post Title exists, Insert post if doesn’t, Add Incremental # to Meta if does
- What is the index [0] for on post meta fields?
- How to update_post_meta value as array
- Adding meta tag without plugin
- What’s the point of get_post_meta’s $single param?
- What is the different between an attachment in wp_posts and an attachment in wp_postmeta?
- How to edit a post meta data in a Gutenberg Block?
- Sanitizing integer input for update_post_meta
- Execute action after post is saved with all related post_meta records (data)
- Lack of composite indexes for meta tables
- How can I retrieve multiple get_post_meta values efficiently?
- Get a single post by a unique meta value
- if get_post_meta is empty do something
- How we get_post_meta without post id
- How get post id from meta value
- What is the code to get the download link for a product in WooCommerce?
- Safe to delete blank postmeta?
- Custom field metabox not showing in back-end
- advanced custom fields update_field for field type: Taxonomy
- Action hook on Edit custom post type?
- update_post_meta not saving when value is zero
- Meta compare with date (stored as string) not working
- How to hide meta box values from custom fields list?
- Trying to get custom post meta through Jetpack JSON API [closed]
- How to update/insert custom field(post meta) data with wordpress REST API?
- get registered metaboxes by post type or post ID
- How do I remove all the metaboxes for a custom post type?
- Better way to enforce category hierarchy in post_categories_metabox?
- get_post_meta returning empty string when data shows in the database
- publish_post action hook doesn’t give post_meta_data
- Remove WordPress.org Meta link
- Remove post meta keys
- How to access the post meta of a post that has just been published?
- Why time functions show invalid time zone when using ‘c’ time format?
- How to get meta box data to display on a page
- Save metabox with multiple checkbox array
- esc before saving or before displaying does it matter?
- Why is get_post_meta returning an array when I specify it as single?
- How to batch update post content with custom post meta value
- How to update/delete array in post meta value?
- How to get all term meta for a taxonomy – getting term_meta for taxonomy
- Add a meta description to home page?
- Get all posts from custom post type and insert in select input as metabox
- Why can’t I hook into save_posts after admin_init?
- Detect meta value changes when post is updated (post_updated)
- Theme elements not translating
- delete unused postmeta
- Should I sanitize custom post meta if it is going to be escaped later?
- add_meta_boxes action with refresh on save
- Add post meta based on another post meta value before publish post
- Change meta tags programatically
- How do I retrieve multi-dimensional arrays from the wp_postmeta table, & display on a website?
- Check if meta key value already exists
- Front-end update_post_meta snippet displays white screen?
- Query between two meta values?
- Save both current and new version of post meta
- Get Advanced Custom Fields values before saving [closed]
- Give extra post-meta to RSS feeds
- How to get meta value in wp_attachment_metadata
- WP REST API “rest_no_route” when trying to update meta
- Clean up output added via wp_head()
- List posts under meta_value heading
- Create meta boxes that don’t show in custom fields
- Why am I getting an infinite loop with have_posts?
- get_post_meta – get a single value
- delete value 0 in post meta [closed]