PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback

Question

This is error:

PHP Warning:  call_user_func_array() expects parameter 1 to be a valid callback, class 'App\Bootstrap' does not have a method 'monsterinsights_vue_get_notifications' in /home2/*****/public_html/wp-includes/class-wp-hook.php on line 307

This is the class-wp-hook.php file on line 307:

            // Avoid the array_slice() if possible.
            if ( 0 == $the_['accepted_args'] ) {
                $value = call_user_func( $the_['function'] );
            } elseif ( $the_['accepted_args'] >= $num_args ) {
                $value = call_user_func_array( $the_['function'], $args ); ---> this is line 307
            } else {
                $value = call_user_func_array( $the_['function'], array_slice( $args, 0, (int) $the_['accepted_args'] ) );
            }

Can you please help me resolve the error. Thanks :)