Thanks for the help Steve, I removed scope from the code and that solved all of the issues. One last question and you can close this one, how do I set a default selection for the taxonomy dropdown?

Hello Steve, thanks for the reply, the parts/terms is in the plugin, this plugin also creates the mro_project post type through the piklist method. I made some edits to the field code and moved it into the meta box section and it works there. I’m not sure why its not working in the terms folder, but using it in the meta box will work for me, though its now giving me this warning.

Warning: array_column() expects parameter 1 to be array, object given in <plugin_path>/piklist/includes/class-piklist.php on line 2524

Oh never mind I found out what the issue was actually, the meta_map_cap had the wrong “‘” around them that messed up the code! Sorry for the unnecessary topic.

There aren’t any duplicates of that field name from what I see, I know that my WordPress version is a bit behind if that would effect anything.

Thanks Steve, I was able to get the meta box to display everything. But there still seems to be a problem. When I try to add a user in the form I created in this metabox to add to this specific project (an attendee table linking to the project ID the edit page is on), the POST method does not work. I know that GET works because I can use it for the ‘Remove Users’ links that are generated under the OPTIONS column of my table if there are attendees already in the database from user registration.

Here is the code and the main parts that are causing the problem are this part here –

<?php
// Process add form if sent
		  if(isset($_POST['mro_add_user'])) {
			  $_POST = stripslashes_deep($_POST);
			  $add_username = $_POST['mro_add_user'];
			  if (username_exists($add_username) != NULL) {
			  	// Check not already registered
				$add_userid = username_exists($add_username);
				$extra_userdata = get_userdata($add_userid);
				$add_firstname = $extra_userdata->first_name;
				$add_lastname =  $extra_userdata->last_name;
				$a_registered = $wpdb->get_var("SELECT user_id FROM ".$wpdb->prefix."mro_attendees WHERE event_id = ".$project_id." AND user_id = ".$add_userid);
				// If not already registered
				if ($a_registered == "") {
					$user_comment = $_POST['mro_add_comment'];
					$wpdb->insert($wpdb->prefix.'mro_attendees', array( 'event_id' => $project_id, 'user_id' => $add_userid, 'user_first_name' => $add_firstname, 'user_last_name' => $add_lastname, 'user_comment' => $user_comment ) );
					?>
                    <div class="updated"><p><strong><?php _e('User ' . $add_username . ' added.' ); ?></strong></p></div>
                    <?php
				} else {
					?>
            		<div class="updated"><p><strong><?php _e('User ' . $add_username . ' already on list.' ); ?></strong></p></div>
            		<?php
				}
			} elseif(username_exists($add_username) == NULL) {
				?>
				<div class="updated"><p><strong><?php _e('User ' . $add_username . ' not found.' ); ?></strong></p></div>
				<?php
			}
			  
		  }
		  ?>

Along with this –

<p style="clear:both;">&nbsp;</p>
		  <p style="clear:both;"><strong>Add Participant by wordpress username:</strong>	      </p>
		  <form id="add_user" name="add_user" method="post" action="post.php?post=<?php echo $project_id; ?>&action=edit">
            <p>
              <label for="mro_add_user"></label>
              Username<br />
  <input name="mro_add_user" type="text" id="mro_add_user" size="40" maxlength="150" />
            </p>
            <p>Comment<br />
              <label for="mro_add_comment"></label>
              <input name="mro_add_comment" type="text" id="mro_add_comment" size="40" maxlength="40" />
</p>
            <p>
              <input type="submit" name="mro_add_user_submit" id="mro_add_user_submit" value="Add User" />
            </p>
  </form>

And this is the whole metabox for reference –

<?php
/*
Title: Attendee Information
Post Type: mro_project
Order: 3
*/
?>
<?php $project_id = get_the_ID(); ?>
<?php
// Process add form if sent
		  if(isset($_POST['mro_add_user'])) {
			  $_POST = stripslashes_deep($_POST);
			  $add_username = $_POST['mro_add_user'];
			  if (username_exists($add_username) != NULL) {
			  	// Check not already registered
				$add_userid = username_exists($add_username);
				$extra_userdata = get_userdata($add_userid);
				$add_firstname = $extra_userdata->first_name;
				$add_lastname =  $extra_userdata->last_name;
				$a_registered = $wpdb->get_var("SELECT user_id FROM ".$wpdb->prefix."mro_attendees WHERE event_id = ".$project_id." AND user_id = ".$add_userid);
				// If not already registered
				if ($a_registered == "") {
					$user_comment = $_POST['mro_add_comment'];
					$wpdb->insert($wpdb->prefix.'mro_attendees', array( 'event_id' => $project_id, 'user_id' => $add_userid, 'user_first_name' => $add_firstname, 'user_last_name' => $add_lastname, 'user_comment' => $user_comment ) );
					?>
                    <div class="updated"><p><strong><?php _e('User ' . $add_username . ' added.' ); ?></strong></p></div>
                    <?php
				} else {
					?>
            		<div class="updated"><p><strong><?php _e('User ' . $add_username . ' already on list.' ); ?></strong></p></div>
            		<?php
				}
			} elseif(username_exists($add_username) == NULL) {
				?>
				<div class="updated"><p><strong><?php _e('User ' . $add_username . ' not found.' ); ?></strong></p></div>
				<?php
			}
			  
		  }
		  ?>
		<?php
		  // Process remove if sent
		if (isset($_GET['remove_attendee'])) {
			$remove_attendee = (int)$_GET['remove_attendee'];
		} else {
			$remove_attendee = '';
		}
          if ($remove_attendee != '') {
			$wpdb->query("DELETE FROM ".$wpdb->prefix."mro_attendees WHERE id = $remove_attendee");
			$place = $_GET['place'];
			?>
            <div class="updated"><p><strong><?php _e('Attendee '.$place.' removed.' ); ?></strong></p></div>
            <?php
		  }
		  ?>

<h4>Event Participants:</h4>
<p><table width="auto" border="0" align="left" cellpadding="5" cellspacing="5">
	<tr>
		<th align="left" scope="col">Participant #</th>
		<th align="left" scope="col">Username</th>
		<th align="left" scope="col">First Name</th>
		<th align="left" scope="col">Last Name</th>
		<th align="left" scope="col">Email</th>
		<th align="left" scope="col">Comment</th>
		<th align="left" scope="col">Options</th>
	</tr>
	<?php
	$users = $wpdb->get_results("SELECT id, user_id, user_first_name, user_last_name, user_comment FROM ".$wpdb->prefix."mro_attendees WHERE event_id = ".$project_id." ORDER BY id ASC");
	$num = 1;
foreach ($users as $user) {
	$user_info = get_userdata($user->user_id);
	?>
	<tr>
		<td><?php echo $num; ?></td>
		<td><?php echo $user_info->user_login; ?></td>
		<td><?php echo $user_info->first_name; ?></td>
		<td><?php echo $user_info->last_name; ?></td>
		<td><a href="mailto:<?php echo $user_info->user_email; ?>"><?php echo $user_info->user_email; ?></a></td>
		<td><?php echo $user_info->user_comment; ?></td>
		<td><a href="post.php?post=<?php echo $project_id; ?>&action=edit&remove_attendee=<?php echo $user->id; ?>&place=<?php echo $num; ?>">Remove User</a></td>
	</tr>
	<?php
	$num++;
	}
	?>
</table></p>
	<p style="clear:both;">&nbsp;</p>
		  <p style="clear:both;"><strong>Add Participant by wordpress username:</strong>	      </p>
		  <form id="add_user" name="add_user" method="post" action="post.php?post=<?php echo $project_id; ?>&action=edit">
            <p>
              <label for="mro_add_user"></label>
              Username<br />
  <input name="mro_add_user" type="text" id="mro_add_user" size="40" maxlength="150" />
            </p>
            <p>Comment<br />
              <label for="mro_add_comment"></label>
              <input name="mro_add_comment" type="text" id="mro_add_comment" size="40" maxlength="40" />
</p>
            <p>
              <input type="submit" name="mro_add_user_submit" id="mro_add_user_submit" value="Add User" />
            </p>
  </form>
		  <p style="clear:both;"><strong>Participant Emails:</strong></p>
		  <p>To keep the page simple, no mass emailer is included in this section. If you really want to email everyone you can copy the list below into your BCC to field and email them that way.</p>
		  <blockquote>
		    <p><?php 
			 $num = 1;
	foreach ($users as $user) {
		$user_info = get_userdata($user->user_id);
		  echo $user_info->user_email . ", ";
			$num++;
		}
	?></p>
  </blockquote>

Yeah, that was it, I was copying code from one file to another and forgot the closing bracket. Thanks for the catch!