Display Message Button only when a user is logged in.

um-message.php

remove_action( 'um_profile_navbar', array( UM()->Messaging_API()->profile(), 'add_profile_bar' ), 5 );
add_action( 'um_profile_navbar', 'custom_add_profile_bar', 6 );


function custom_add_profile_bar( $args ) {
		$user_id = um_profile_id();

		if ( is_user_logged_in() ) {
			if ( get_current_user_id() == $user_id ) {
				return;
			}

			if ( ! UM()->Messaging_API()->api()->can_message( $user_id ) ) {
				return;
			}
		}

		wp_enqueue_script( 'um-messaging' );
		wp_enqueue_style( 'um-messaging' ); ?>

<?php if ( is_user_logged_in() ) : ?>
		<div class="um-messaging-btn">
			<?php echo do_shortcode( '[ultimatemember_message_button user_id="' . $user_id . '"]' ) ?>
		</div>
<?php endif; ?>
		<?php
}