Ultrasonic Tranducer 400ET/R180 for 400ST/R

Hi guys, my project is on an ultrasonic motion detector, i m using the circuit from https://kitrus.com/kits.html. but i couldnt get my hands on the 400S series so i m using the 400E series. Obviously my circuit is not working as it should. plzzzz what changes could the change in the tranducers cause.
Also wats the 10M in parallel with the tranducer for.

The link doesn't work and you haven't posted a schematic.

He keeps making duplicate threads for his project.
The kit maker does not have a manufacturer's name nor a datasheet for the substitute transducers he is using.
The kit is this one: https://www.electro-tech-online.com/custompdfs/2010/03/k49.pdf