If you have the original sketch that someone wrote for the logger, then that should give you clues of how everything should be connected. There are several different ways in which to connect a tipping bucket to a Mayfly logger, some require a circuit in between to do the actual counting (like the Trinket or an ATtiny), but we’ve had good luck with just connecting the two poles of the tipping bucket switch directly to the Mayfly board and using digial pin 10 (D10) which is a hardware interrupt pin to wake the logger and count the tip. By activating the onboard pullup resistor (using jumper SJ12) you can just connect one wire of the bucket to D10 and the other to Mayfly ground. There’s a full explanation in this thread (https://www.envirodiy.org/topic/rain-gauge-tip-data-without-rain/) along with the sample code. However, note the one drawback to using this method (as mentioned in that thread) that tips won’t be counted if the Mayfly is busy doing something else like making a radio or cell transmission, so an occasional tip might be missed during high rain-rate events (and depending on your transmission frequency). So having a separate counting device report tips to the Mayfly on demand is a more reliable and accurate method, so people use the Trinket, ATtiny, or other small affordable programmable chip for that.