Sorry to say, we had an oops on the first run of production boards. Solder mask was applied to the area where the copper pipe antenna must be soldered to the board.
Using a hobby knife or Dremmel tool, carefully remove the mask from this area. This is the large rectangular pad on the left-hand side of the board. The pad is on the top and the bottom of the board. The area is circled in the layout below. Since how you attach the pipe depends on the tools and method you use (explained in the construction steps that follow later), you may wish to read ahead and decide how the pipe will be attached. In most cases, only one side of the pad will need to have the mask removed.