Installing a slot drain afterwards, any experiences?

Okay. But how does the channel then help the water to drain on the horizontal slabs? And as I said: If the water is standing lengthwise on the left side, you also need a channel on the left side, lengthwise. You would need a channel with integrated slope.

I would logically remove and relay the slabs at that spot. The last row would have the slope towards the channel. Regarding the slope of the channel, I was thinking of a slot drain from ACO. They have a minimal slope built in.

I still don’t understand the placement.
You want to slope the last row in front of the lawn towards the terrace, and then go back towards the lawn over a slot drain? Do I understand that correctly?
Is the water now coming from the lawn or from the terrace?

I still don't understand the placement. You want to slope the last row in front of the lawn towards the terrace and then go back towards the lawn via a slot drain? Am I understanding that correctly? Is the water coming from the lawn or from the terrace?

The water comes from the terrace and flows towards the lawn. I would like to place the drain as shown in the picture (red line) so that the water can flow directly into the soakaway. The last row of slabs would have a slope towards the drain so that the water does "not" flow onto the lawn.

And the gutter after the last row, before the lawn? Would look better. Or do you then merge the last row into the lawn?