I upgraded my V.4 firmware to 5.01 and added WiFi. I successfully set WiFi up and can access the OpenEVSE webserver on my local net at its assigned IP or by DNS at http://openevse/. I then set up an account at http://data.openevse.com/emoncms, set the Node to 0, and entered the Emoncms read/write api key as listed in my Emoncms account.
I set up a new Device in Emoncms at Node:0 and type:OpenEVSE, which generated a different device access key. From elsewhere on this forum it seemed I needed to use the R/W key from my account page or as shown on the Devices Help page. However, the key in the Devices list is the one that works.
Thank you for sharing this information. I had exactly this issue, trying to get OpenEVSE connected to EMONCMS.
I shared the link to your post and here is the issue it helped resolve.