Response status code 503 generally means the service is unavailable.
This could mean that the server can't handle the requests because of technical issues. In which case web scrapers should be paused to prevent being IP blocked for too many invalid repeated connections.
Alternatively, 503 status code is also used to block web scrapers if they are identified and undesired.
To avoid status code 503 when web scraping we should ensure that the server cannot identify the web scraper connections. For that refer to our how to scrape without being blocked guide which covers all of the ways to prevent web scrapers from being identified.