By default, WordPress Media Library (used for attachments) allows file uploads only for users who have the upload_files capability. So, everyone who doesn’t have this capability (e.g. a subscriber) will receive an error on trying to upload a file.

To add this capability to subscribers you can e.g. use the User Role Editor plugin. Just enable the upload_files capability for the users which need it and it will work.

Other option is to add this capability dynamically via a hook. To do this you can add e.g. this code to your theme’s functions.php:

            function give_permissions( $allcaps, $cap, $args ) {
                $allcaps['upload_files'] = true;
                return $allcaps;
            }
            add_filter( 'user_has_cap', 'give_permissions', 0, 3 );     

Basically, it enables the upload_files capability to everyone – but you can extend this logic to allow it only for certain users at certain moments.

By default WordPress does not allow this. Reason is: logged out user has no ID (id is 0), and no permissions/capabilities enabled for him.

A solution would be to create an actual user that will be used as a single user for all logged-out users, and copy his ID (e.g. id = 100).

Then you can add a simple hook to identify logged out users as User with ID 100. To do this you can use a hook like this:

    function set_loggedout_id( $user_id ){
       if( empty( $user_id ) ){
          $user_id = 100;
       }
       return $user_id;
    }
            
    add_filter( 'determine_current_user', 'set_loggedout_id', 999, 1 );

Basically, it “tells” WordPress to replace the empty ID of a logged out user with a value of 100.
Then you can allow uploading for this user.

When you are moving on live site from local or stage site we can suggest to use Plugin Duplicator. We use it and it’s working fine, because he will transfer all the files and also the tables to database.

You have some conflict with theme or other plugin. Please insert this in Custom wpDataTables CSS under the “Custom JS AND CSS” in main settings of wpdatatables.

.wpdt-c .modal{ width: inherit !important ; background-color: initial !important; }