Set a value of a text input in a repeat with a flow

So this has been bugging me for a few hours now.
I have a repeating table that has in there a couple of selects and a couple of inputs.
what I need to do is on the select, run flow and depending on the category chosen it does the action, have no problems there.
This issue I am having is on lets say subcat=3 then I need to add the value of 1000 to the input in the relevant row.
I have the inputs id as int_sel_boxQTY_0, int_sel_boxQTY_1, int_sel_boxQTY_2 etc
but for some reason the flow just will NOT add the value to it.

the action on the flow is

run: {action: "{{(inp_sel_boxQty_$param.index).setValue(1000)}}", output: true}

but it will just not work, can anyone shed some light on where I am going wrong please.