Source

File: wp-includes/rest-api/fields/class-wp-rest-meta-fields.php

protected function delete_meta_value( $object_id, $meta_key, $name ) {
		$meta_type = $this->get_meta_type();

		if ( ! current_user_can( "delete_{$meta_type}_meta", $object_id, $meta_key ) ) {
			return new WP_Error(
				'rest_cannot_delete',
				/* translators: %s: Custom field key. */
				sprintf( __( 'Sorry, you are not allowed to edit the %s custom field.' ), $name ),
				array(
					'key'    => $name,
					'status' => rest_authorization_required_code(),
				)
			);
		}

		if ( ! delete_metadata( $meta_type, $object_id, wp_slash( $meta_key ) ) ) {
			return new WP_Error(
				'rest_meta_database_error',
				__( 'Could not delete meta value from database.' ),
				array(
					'key'    => $name,
					'status' => WP_Http::INTERNAL_SERVER_ERROR,
				)
			);
		}

		return true;
	}