I tried to build this project in PlatformIO for quite some time. It compiled fine, flashed fine to the m5stack, and I could successfully connect to the AP, but the webpage simply wouldn't load no matter what I did. After some troubleshooting I determined that the client.flush() around line 120 was causing the issue:
if (readyResponse) // отдать браузеру
{
String GET = parseGET(currentString);
//client.flush();
After commenting this out the project works fine. I'm using the latest Chrome for Android for testing this, but also used Chrome on a Windows 10 PC and had the same result. The webserver simply gave an empty response.
Hope this helps someone else work through this example!