Optiminer: "Required argument 'stratum' is missing

Hi guys!

I am quite new to the mining scence. After coming across some articles about gpu mining, I set up an old computer with a used R7 370 2Gb just for fun.

As 2GB Vram dont seem to be enough for ethereum anymore, I am now trying my luck with Zcash.
Unfortunatly that is not working.

I installed zcash 1.7.0, create a t- and z-adress and the zcashd successfully starts and validates transactions.
Now I want to mine coins with optiminer-zcash, but it always promts me:

[error] Required argument 'stratum' is missing.

Anyone an idea how to solve that?
It does not matter how I configure my zcash.conf, the error message is always the same.

And btw: What is that RPC stuff? I have no idea what "username" to us and where to register if needed..