i found https://www.domoticz.com/forum/viewtopic.php?t=7840
and gizmocuz worte
you should use/request the V_VAR1 when your node starts (powers up), so the last counter value is retrieved
dont send anything until you got this
and
you need to send to domoticz the counter value, this counter need ...

rain sensor is a simple ON/OFF switch.... it is NOT a rain gauge

are you talking about a rain gauge (a device that counts mm2 of rain in a specific area....)?
for gauge you have to follow the syntax:
&nvalue=0&svalue=RAINRATE;RAINCOUNTER where
RAINRATE = amount of rain in last hour in [mm x 100 ...

What mark&type of rain sensor are you using?

Interfacing as rain gauge to RFXCom or to RFLinkGateway?
If Yes, you probably already read the data to a Device of Domoticz, but did you activate the Device in Setup/ List of Devices?
If No, what kind of integration/interfacing are you planning for ...

Rain sensor - how it works ?
Hi
I try to run rain sensor, and i can't understand how it works
i use json command to update sensor.

So
Sensor idx = 10

Day 1
no rain
What should i Send to domoticz to report no rain ?

http://localhost:8080/json.htm?type=command&param=udevice&idx=10&nvalue=0&svalue=0 ...