@Craig127,
Out of curiosity, why not use the Matter connectivity to interact with the devices through official means?
I would honestly recommend taking a look at the Home Assistant development for help, as they will know far more about interacting with the backend connections than our team does.
I believe that the credentials should be the same login used to log into your Kasa and Tapo App, along with the credentials used to log into the forum - so please be careful. I believe that HA has seen problems if your username and password contain capitals, but once again I am not sure - and I would recommend poking around their forums for any unofficial development out there.