Adding metaboxes to attachment pages

get_post_meta returns an array when you set the 3rd parameter to false, so $value is an array in your metabox callback and you’re treating it as string. I assume an attachment has a single value for license, so you want to set that to true instead.

Related Posts:

  1. How do I get attachment_id?
  2. Put the media uploader in a metabox
  3. Display Single Attachment Image file size, uploaded date, resolution, file-name etc in Sidebar
  4. save_post not working with attachments
  5. Show how many images are attached to a post/page on compose page
  6. dynamically get post attachment while editing
  7. Create more Meta Boxes as needed
  8. Set Default Admin Screen options & Metabox Order
  9. How to set default screen options?
  10. Passing error/warning messages from a meta box to “admin_notices”
  11. Add “upload media” button in meta box field
  12. Can I add a Category Metabox to attachment?
  13. Add a Meta Box for uploading a SECOND Featured Image?
  14. Does WordPress have a “Form API”?
  15. Metabox with checkbox is not updating
  16. How to HIDE everything in PUBLISH metabox except Move to Trash & PUBLISH button
  17. What is the “Advanced” $context in add_meta_box?
  18. Removing panels (meta boxes) in the Block Editor
  19. Change The Title Of a Meta Box
  20. WordPress SEO by Yoast: Hide Meta Boxes in Posts for Non-admins
  21. How to make open/closed and hidden/shown metaboxes status saved on a per-post basis?
  22. How To Remove The “+ Add New Category” Link From A Category Metabox
  23. How can I create a taxonomy meta-box with search suggestions but no new terms input?
  24. Remove the Featured Image Meta Box
  25. Remove the Yoast SEO Post Metabox [closed]
  26. Best practices for meta box placement?
  27. Creating a metabox to upload multiple images
  28. How Does WordPress Remember Metabox Positions?
  29. Sample code for validating custom metabox?
  30. Post custom metabox textarea using wp_editor
  31. How to Add Reminders/Notes to New Post Meta Boxes
  32. Removing Metabox for “Slug” without removing functionality
  33. How to reorder meta box position?
  34. Prevent sorting and dragging of specific postbox metabox
  35. One metabox for multiple post types
  36. How do I position meta_box on post edit screen after the title?
  37. How to add a class to meta box
  38. Has anyone successfully integrated qtranslate with custom metaboxes?
  39. Custom Meta Boxes: multiple fields within a repeatable field
  40. Removing meta boxes: remove-meta_box() or unset()?
  41. Save checkbox value in metabox
  42. How to group meta boxes on the post edit page
  43. Use meta box drag and drop to order items independently
  44. inside a metabox
  45. Add Meta box Befoure Post Title
  46. Hiding a theme’s meta box
  47. Metabox date month number to word
  48. get registered metaboxes by post type or post ID
  49. Remove metabox from specific page template in admin
  50. Is there a filter/action to add content to WP admin metaboxes?
  51. Attach Files Metabox
  52. CMB2 metabox conditional logic
  53. Tinymce/WordPress is removing all line-breaks?
  54. How do I create a meta box for dates?
  55. Adding submit or update button to custom metabox?
  56. Editing the Default Links like “Site Admin” in the Sidebar Meta Section?
  57. How to pass variable via $callback_args for add_meta_box
  58. Undefined function error when creating Custom Meta Box
  59. How to get meta box data to display on a page
  60. custom fields for attachments?
  61. esc before saving or before displaying does it matter?
  62. Block metabox – No expanding, no moving around
  63. wp_generate_attachment_metadata gives me an empty array
  64. Move excerpt to always be directly below post content in admin
  65. Access the environment of an admin page from another admin page
  66. Add a meta description to home page?
  67. Editing Screen: Make Update or Publish Button Follow The Page
  68. Removing custom meta box added in parent theme
  69. Add multiple images to a page sidebar
  70. Add filter ‘wpautop’ to meta box textarea
  71. Use meta box value in CPT as post title
  72. Custom “Publish” / “Update” button &
  73. Why can’t I hook into save_posts after admin_init?
  74. Meta Boxes in Front End Post Submission Form
  75. Getting the ID of a meta box
  76. how to sanitize checkbox input?
  77. add_meta_box does not go ‘side’
  78. Custom filter for the_content doesn’t work correctly
  79. Remove a plugin meta box from the dashboard
  80. How to insert Gallery shortcode to a meta box
  81. Getting jQuery sortable items in custom metabox
  82. Custom meta box shown when template is chosen [duplicate]
  83. Modifying the main editor priority
  84. How to make a meta box field a requirement
  85. Check if meta key value already exists
  86. How to make multicheck for post/page meta box
  87. Display list of tags as drop down menu or radio buttons in a meta box?
  88. Adding uploaded images to editor from metabox instead of default popup uploader
  89. How do I stop HTML entities in a custom meta box from being un-htmlentitied?
  90. Is there a predefined callback function for custom categories?
  91. Choosing a default page tempate (Classic => Gutenberg)
  92. meta content on required pages
  93. How to List all Sidebars in a Metabox
  94. How to remove the RichText Meta Box
  95. Set height of the categories meta box in post dashboard
  96. Conditional Meta Boxes
  97. Why is `add_meta_box` not working?
  98. How to access global $wp_meta_boxes variable on front-end?
  99. get_post_meta doesn’t work
  100. PHP Warning: call_user_func() expects parameter 1 to be a valid callback