Need some help debugging code for Ultrasonic Tank Sensor

Hello everyone, my first post. In github there is this code https://github.com/frewie/UltrasonicTankSensor.git - which allows for an ultrasonic tank sensor to be connected to the underside of a tank, the sensor sends a ping through the tank to the top of the fluid level and gives the time taken for the ping to return to the sensor thereby measuring height, from which volume can be calculated. This information is then sent to SignalK. The code is a little old - may have been written prior to SensESP v2. I'm new to coding and can't get the code to compile, even when pegging all dependent library versions. (I'm looking to run this on a ESP-32 board.) I've also tried to uplift the code to SensESP 2 following the guidance on the SignalK site, but no luck. I've spent a number of days on this and I'm sure someone will be able to take a quick look and spot the issue right away! Can anyone help me please?