Arduinos connected using I2C ?

I have 2 arduinos (for now will be adding more) connected using I2C. I have a Master reader and slave writer. I am using the Slave to tell me the Master when a function is called. I have a web server off the master with a checkbox whether that function has been called. I am have the code to read the checkbox being unchecked or checked. I want to trigger a relay connected to my slave through my webserver checkbox connect to the Master.

I am lost how to send data from the master reader to the slave to trigger a fuction

OK. Nice plan. But what is your question?

Sorry. My question was what is the easiest way to send data from the master reader back to the slave to trigger a function.

Take a look to this tutorial first - https://www.arduino.cc/en/Tutorial/MasterWriter
Then you instead of printing received byte you can code in it function number you want to invoke.

I am using the master to read already. Will i be able to use write as well??

Rumble25:
I am using the master to read already. Will i be able to use write as well??