Nested Repeater

I'm trying to turn a widget into a nested repeater.

The Green container is a repeater and the lavender container is a nested repeater, which itself has a price repeater. I'm trying to port an MVP application i was able to create on wordpress using advanced custom fields. So far i was able to get this code to work for a simple text widget repeater:

int formFieldRepeater(List<int>? formFieldCountList) {

  return (formFieldCountList!.last + 1);
}

Any ideas of making this work?

Thanks