interesting to know that checksum computes. Maybe then the rest of the code doesn’t proceed correct, when it reads the values, becuase when 1st byte is 0xFF it double prints output. However when it has two times the 0xFF it outputs the ERROR. The output is on browser whn I hit the IP, so maybe serial doesnt matter.
Utrasonic.h is there because I have also tried other ultrasonic sensor with similar code tha works (but it doesnt need UART but only pin 3)