Thanks for reporting this! It seems to be an inconsistency in the server configuration after the recent Cloud 1.55 release. The "online book" (Elementary Introduction to the Wolfram Language) and the documentation center are pointing to the wrong URLs. We're working on a fix.

In the meanwhile, you can reach the book directly here: https://www.wolfram.com/language/elementary-introduction/2nd-ed/ and the Documentation Center is available here: https://reference.wolfram.com/language/

Sorry for the inconvenience.

I changed also DNS configuration. No solution. www.test.wolfram.com is not resolved! C:\Users\Chris>ping www.test.wolfram.com Ping request could not find host www.test.wolfram.com. Please check the name and try again.

C:\Users\Chris>ping www.wolframcloud.com

Pinging www.wolframcloud.com [140.177.16.83] with 32 bytes of data: Reply from 140.177.16.83: bytes=32 time=115ms TTL=48 Reply from 140.177.16.83: bytes=32 time=116ms TTL=48 Reply from 140.177.16.83: bytes=32 time=122ms TTL=48 Reply from 140.177.16.83: bytes=32 time=116ms TTL=48

Ping statistics for 140.177.16.83: Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), Approximate round trip times in milli-seconds: Minimum = 115ms, Maximum = 122ms, Average = 117ms