Custom field not updating when value is empty

You are checking if the field is empty. Try to update it if its empty as well

 if( trim( $attachment[ $field ] ) == '' ) $post[ 'errors' ][ $field ][ 'errors' ][] = __( 'Error! Something went wrong.' );
 else update_post_meta( $post[ 'ID' ], $key, $attachment[ $field ] );

Try 

if( isset( $attachment[ $field ] ) ) {
            if( trim( $attachment[ $field ] ) == '' )
            $post[ 'errors' ][ $field ][ 'errors' ][] = __( 'Error! Something went wrong.' );
            endif;
            update_post_meta( $post[ 'ID' ], $key, $attachment[ $field ] );
        }

Related Posts:

  1. Display info from custom fields in all images’ HTML
  2. copy attachments to another post type and change attachment url
  3. ajax delete value from custom field array
  4. Save attachment custom fields on front end
  5. Media Attachment Custom Meta Fields not saving in Media Uploader when using jQuery UI Autocomplete
  6. Can I exclude a post by meta key using pre_get_posts function?
  7. What is the index [0] for on post meta fields?
  8. Best way to programmatically remove a category/term from a post
  9. Custom field metabox not showing in back-end
  10. So much data in postmeta
  11. How to hide meta box values from custom fields list?
  12. get_post_meta() unserialize issue – returns boolean(false)
  13. What is the advantage of the wp_options design pattern?
  14. How can I remove fields in the attachment editor?
  15. display specific custom fields
  16. Meta keywords and descriptions plugin for manually editing meta for each page/post
  17. Multiple meta values for same meta_key adding on “Preview Changes” hit but not on saving or updating post
  18. Up/Down voting system for WordPress
  19. post meta data clearing on autosave
  20. Create custom field on post draft or publish?
  21. Update meta values with AJAX
  22. Cannot edit post meta fields with rest API
  23. Add a post meta key and value only if it does not exist on the post
  24. Custom fields to save multiple values
  25. Function to change meta value in database for each post
  26. wp_handle_upload error “Specified file failed upload test” but still creates attachment?
  27. Which is best in the following scenario : post_meta vs custom table vs parent/child posts
  28. Saving custom image meta fields
  29. Get all meta keys assigned to a post type
  30. using multiple meta_key and meta_value in query_posts
  31. Adding custom fields (post meta) before/during wp_insert_post()
  32. How to query posts with certain custom meta data, and output Post data
  33. ACF: How to get the full field name (meta_key) by a field key?
  34. post meta getting deleted on save
  35. How to add a new meta key and assign timestamp to posts
  36. Validate data on attachment_fields_to_save
  37. meta_compare seems to be treating values as strings instead of integers as expected
  38. Limit the number of acf content when displaying in post loop [closed]
  39. Read / Watch / Listen times – meta
  40. How to add custom metadata text box dropdown to sidebar in Gutenberg editor for all post types
  41. How do I Implement Atomic Update of Post Metadata?
  42. Why is my Custom Meta Box Field Inputs NOT saving?
  43. Get registered custom fields or post meta even if empty
  44. Displaying multiple URLs as custom field values
  45. Show values of custom post meta on ‘Add new post’ page?
  46. Custom post meta field effect on the performance on the post
  47. Limits, not all post are showen when querying for posts by view count
  48. Display Custom Meta Box Field Only If Value is Present
  49. Stop sending email everytime I updates my post
  50. Best way to store everyday post views?
  51. shortcode in a custom metabox
  52. Unable to get specific value from post meta
  53. Problem with saving large amount of data in postmeta/usermeta
  54. Custom meta is not being saved
  55. Link FROM attachment to full post and get custom fields values on attachment page?
  56. How to get posts with a metadata numeric key greater than X?
  57. IF Custom field value equals ZERO
  58. How to use media upload on metabox post page without breaking TinyMCE?
  59. Let’s Create Custom Field Template Documentation
  60. Branch made by several custom values
  61. Looping inside block return
  62. WordPress creates new lines in postmeta table on post update
  63. User customising position of WordPress Featured Image
  64. Can I save post meta programatically without setting metaboxes?
  65. Insert image into sub-field with update_post_meta
  66. Show custom field on attachment page?
  67. How to use conditional statement with custom field
  68. Save attachment ID instead of URL in custom field
  69. Meta box values are displayed on Custom Fields list. Is it possible to hide them?
  70. Best way to achieve multiple links in a post title
  71. Display Meta Data with HTML?
  72. How can I add/update post meta in a admin menu page?
  73. Get author total post votes from post meta
  74. Group Posts By Custom Meta Value: Date
  75. custom filed from post in the side bar
  76. How to display custom fields in hestia theme
  77. Shortcode for Custom Field of Media Attachment (to use with Featured Images)
  78. Custom field in media library not saving, selected() function not adding “selected” to select list input type
  79. How to speed up post list slowed by update_meta_cache()?
  80. WordPress Blocks, setAttributes not saving
  81. Adding Facebook’s image and meta description retrieval capabilities to a WordPress post
  82. SQL query to change the value of a Custom Field
  83. Custom meta POST request fired twice when updating a post in Gutenberg
  84. Add custom field information to source meta data
  85. Update custom field on page specific to logged in user
  86. Create Meta boxes dynamically
  87. How to delete attachments associated with custom field type when post property changes? [closed]
  88. Delete custom meta
  89. Problem saving meta data
  90. Check if value exists before saving
  91. Get meta value when the page is a blog archive
  92. change attachment custom field onChange event
  93. wordpress simple post multi rating with post_meta and user_meta
  94. wp_postmeta are updated for only one page
  95. Custom fields / meta box output
  96. How can I attach files without using a plugin?
  97. Colecting values from custom field checkboxes and displaying them in the post
  98. Build Array from Input Fields question
  99. How can i put a custom field inside this php
  100. get Custom field label (select/dropdown) on front end
techhipbettruvabetnorabahisbahis forumuedueduseduseduedusedueduedusedusedu