Following ESP32 Gauges Tutorial, compilation error

I am trying to follow this tutorial: ESP32 Web Server: Display Sensor Readings in Gauges | Random Nerd Tutorials

I have put everything exactly as mentioned, with the same src/main.cpp and data folder. However, I am getting this compilation error:

Any help is appreciated.

Duplicate of Solved "AsyncElegantOTA >> collect2.exe: error: ld returned 1 exit status"