If I acces http://< ip >/measurements.xml the screen is blank.
If I access http://< ip >/gen.screenshot.bmp the display of the inverter is shown.
In this post you can see which pages I use to get information of inverter.
For me discovery of device isn’t necessary, only move the ip to the device settings would be more appropriate. I have one inverter, my remark is just for future enhancement. If you plan to add discovery, please leave option to give in ip, because in some situations discovery won’t work (cross VLAN).
I am sure I have older version of the stecagrid inverter. So handling different versions would be good enhancement of your app 
