@Wayne-TP 

Tapo android app version is 3.1.315. 

How do I enter decimal places? as I said the keyboard that is shown has a coma and no decimal point.

  @Wayne-TP 

Ahh, yes there it is, a whole new world lies behind that button (exaggeration). Duh should have spotted that myself, thanks. 

So I put in 0.33204 & 0.18137, and checked the 'Bill for the month', the value was wrong  by a factor of 100. The GBP mis-lead me, it makes you think you have to enter fractions of a pound, when you actually need to enter pence and fractions of pence. So instead of entering effectively £0.33204 it's supposed to be 33.204p, now its fine.  

I was a bit disappointed at first as I thought I was going to have to do this for every device, but when going to do the 2nd device, the option to link it to the 1st devices pay rate settings was a very welcome feature, so it didn't take too long to set them all up.  Might be better on the save of the 1st device to ask to link all the other device automatically too (I'll put a feature request in for that).

Good app and support, thanks.