WP_REST_Request::set_body( string $data )

Source

File: wp-includes/rest-api/class-wp-rest-request.php

public function set_body( $data ) {
		$this->body = $data;

		// Enable lazy parsing.
		$this->parsed_json    = false;
		$this->parsed_body    = false;
		$this->params['JSON'] = null;
	}