Hi Leo;
the sketch I tested times the charging time for the cap from 0 to ViH - then measures with the ADC.
ViH for the ESP8266 and ESP32 is 0.75 * Vcc = 2.5V which is outside the range of the ADC.
I've looked at the Nick Gammon meter and I beilieve that too is aimed at the earlier arduinos.
While the ESP8266 and ESP32 are great devices the ADC's leave a lot to be desired (such as linearity) and the ESP32 (as I found out) can be a challenge for "beginners".
I'd suggest the OP gets a nano and a breadboard, a lot of learning and fun for coppers. However as he "needs" wifi then the WeMOS CAN do the job - but he will need to rewrite a LOT of the sketch- and to make it easier, define the limits of the capacitance he needs to measure.
@marceltim - still there?