Please add the given code in your wplms-customizer.php file in wplms-customizer plugin :
if (!function_exists('vibe_certificate_student_avatar')) { function vibe_certificate_student_avatar( $atts, $content = null ) { $id=$_GET['u']; if(isset($id) && $id){ return get_avatar( $id ); } else return '[certificate_student_avatar]'; } add_shortcode('certificate_student_avatar', 'vibe_certificate_student_avatar'); }
Use shortcode [certificate_student_avatar]