[WordPress] How to add custom field to taxonomy.

.php

<?php
/**
 * Add custom fields to term.
 */
function kaleidpixel_add_term_form_fields() {
	if ( 1 < did_action( 'category_add_form_fields' ) ) {
		return;
	}

	?>
	<div class="form-field term-group">
		<label for="custom_term_meta">
			<?php esc_html_e( 'Example meta field', 'kaleidpixel' ); ?>
		</label>
		<?php wp_nonce_field( 'kaleidpixel_term_meta', 'kaleidpixel_term_meta_nonce' ); ?>
		<input type="text" name="custom_term_meta" id="custom_term_meta" value="">

		<p class="description">
			<?php esc_html_e( 'Enter a text for this field', 'kaleidpixel' ); ?>
		</p>
	</div>
	<?php
}

add_action( 'category_add_form_fields', 'kaleidpixel_add_term_form_fields', 10, 2 );

/**
 * Add table column for term.
 *
 * @param  array $columns Table columns.
 * @return array $columns New table columns.
 */
function kaleidpixel_add_term_table_columns( $columns ) {
	$columns['custom_term_meta'] = __( 'Example meta field', 'kaleidpixel' );

	return $columns;
}

add_filter( 'manage_edit-category_columns', 'kaleidpixel_add_term_table_columns' );

/**
 * Add table content for term.
 *
 * @param string $content     column content.
 * @param string $column_name column name.
 * @param int    $term_id     Term id.
 *
 * @return string
 */
function kaleidpixel_add_term_table_content( $content, $column_name, $term_id ) {
	if ( 'custom_term_meta' === $column_name ) {
		$content = get_term_meta( absint( $term_id ), 'custom_term_meta', true );
	}

	return $content;
}

add_filter( 'manage_category_custom_column', 'kaleidpixel_add_term_table_content', 10, 3 );

/**
 * Add custom fields to term.
 *
 * @param object $term Term data.
 */
function kaleidpixel_add_term_edit_form_fields( $term ) {
	if ( 1 < did_action( 'category_edit_form_fields' ) ) {
		return;
	}

	$term_meta = get_term_meta( absint( $term->term_id ), 'custom_term_meta', true );
	?>
	<tr class="form-field">
		<th scope="row" valign="top">
			<label for="custom_term_meta"><?php esc_html_e( 'Example meta field', 'kaleidpixel' ); ?></label>
		</th>
		<td>
			<?php wp_nonce_field( 'kaleidpixel_term_meta', 'kaleidpixel_term_meta_nonce' ); ?>
			<input type="text" name="custom_term_meta" id="custom_term_meta" value="<?php echo esc_attr( $term_meta ); ?>">

			<p class="description">
				<?php esc_html_e( 'Enter a text for this field', 'kaleidpixel' ); ?>
			</p>
		</td>
	</tr>
	<?php
}

add_action( 'category_edit_form_fields', 'kaleidpixel_add_term_edit_form_fields', 10, 2 );

/**
 * Created term meta.
 *
 * @param int $term_id Term ID.
 */
function kaleidpixel_created_term_meta( $term_id ) {
	if ( ! check_admin_referer( 'kaleidpixel_term_meta', 'kaleidpixel_term_meta_nonce' ) || ! current_user_can( 'manage_categories' ) || 1 < did_action( 'created_category' ) || 1 < did_action( 'edited_category' ) ) {
		return;
	}

	$meta = filter_input( INPUT_POST, 'custom_term_meta', FILTER_SANITIZE_SPECIAL_CHARS );

	if ( is_null( $meta ) && ( true === defined( 'DOING_AJAX' ) && true === DOING_AJAX ) ) {
		$meta = get_term_meta( absint( $term_id ), 'custom_term_meta', true );
	}

	update_term_meta( absint( $term_id ), 'custom_term_meta', $meta );
}

add_action( 'created_category', 'kaleidpixel_created_term_meta' );
add_action( 'edited_category', 'kaleidpixel_created_term_meta' );

/**
 * Rest api init.
 */
function kaleidpixel_rest_api_init() {
	register_rest_field( 'category',
		'meta',
		array(
			'get_callback'    => '_kaleidpixel_rest_api_cb',
			'update_callback' => null,
			'schema'          => null,
		)
	);
}

add_action( 'rest_api_init', 'kaleidpixel_rest_api_init' );

/**
 * Add new fields for rest api.
 *
 * @param array $object Object of the term.
 *
 * @return array|null
 */
function _kaleidpixel_rest_api_cb( $object ) {
	$result = null;

	if ( false !== isset( $object['taxonomy'] ) && 'category' === $object['taxonomy'] ) {
		$result = array( 'custom_term_meta' => get_term_meta( absint( $object['id'] ), 'custom_term_meta', true ) );
	}

	return $result;
}