I did have the same problem but found the posible solution here --> http://gejanssen.com/howto/Slimme-meter-uitlezen/ and look at the bottem of the page. You have to insert a resister of 1 K between rts en tx.

For me that fixed the problem.

Found it... Need to make a harware mqtt device.

Fixed.

I cannot switch de plugwise circle. In the devices i have a B/C/F/E prefix. All values are updated and seems good only switching is not possible.

What have i done wrong ?