post-meta-registration.php

<?php
/**
 * Plugin Name:       Post Meta Registration Test
 * Version:           0.1.0
 * Text Domain:       post-meta-registration-test
 */

function register_post_meta_1() {
	register_post_meta( 'post', 'test_post_data1', array(
    'show_in_rest' => true,
    'single' => true,
    'type' => 'string',
	) );
}
add_action( 'init', 'register_post_meta_1' );

function register_post_meta_2() {
	register_meta(
		'post',
		'test_post_data2', array(
			'type'         => 'string',
			'single'       => true,
			'show_in_rest' => true,
  ) );
}
add_action( 'init', 'register_post_meta_2' );