The 400-499 range of HTTP response statuses is reserved for user or client errors. Many of these statuses can be used for blocking but the 403 Forbidden is the most common one.

Using Apify and Crawlee's default configuration with some best practices generally resolves this blocking problem.

Don't forget that blocking can be accompanied by any HTTP response status. A quite common one is also 503 or simply 200 (which is used for successful response) but with a captcha displayed. If that is the case, simply throw an error (ideally with session.retire()) to initiate a retry request with a new session.

You can learn more about the topic in Web scraping: how to solve 403 errors.