There is a double definition of those macros:

• Captive-Portal-ESP32/src/main.cpp

  Line 15 in 1d34db1

  #define MAX_CLIENTS 4 // ESP32 supports up to 10 but I have not tested it yet

• Captive-Portal-ESP32/src/main.cpp

  Line 56 in 1d34db1

  #define MAX_CLIENTS 4

  
  Nothing serious as the values are the same, but if someone wants to change a value, they might have a hard time figuring out why the change has no effect.

Edit : same goes for subnetmask const:

• Captive-Portal-ESP32/src/main.cpp

  Line 20 in 1d34db1

  const IPAddress subnetMask(255, 255, 255, 0); // no need to change: https://avinetworks.com/glossary/subnet-mask/

• Captive-Portal-ESP32/src/main.cpp

  Line 64 in 1d34db1

  const IPAddress subnetMask(255, 255, 255, 0);