If you get errors in Fritzing when you File/Export/for Production/Extended Gerber, this is what to watch out for.
Export Gerber always wants 2 copper groups, copper0 for the bottom board layer, and copper1 for the top board layer. This is fine for TH (through hole) parts, and they should both be included because a TH part can be used on both 1 sided and 2 sided boards, but for SMT parts only 1 copperX is needed. If you get errors in Export and know it’s a single sided part, you now know which copperX to ignore.
There are no instructions for the XML grouping of the PCB drawing so I had to reverse engineer it from other parts.
From what I gather you need :-
1 - a Silkscreen group with all it’s nodes - superfluous silkscreen writing that does nothing critical -.
2 - a Copper1 group with all contact coppers for the top
3 - and inside that a duplicate of Copper1 renamed to Copper0 for contacts on the bottom for TH parts.
Copper1 and copper0 are interchangeable so long as one is inside the other, if you are doing TH.
–Silkscreen
–Copper0 - bottom
----Copper1 - top
–Silkscreen
–Copper1 - top
----Copper0 - bottom
I’m no XML coding expert so I do it the easy way in Inkscape. I open the XML editor and just duplicate Copper0, rename that Copper1, and just indent it into Copper0, or visa-versa.
Also if a part needs extra holes, like mounting holes, these holes have to be put in the Copper groups or they won’t get drilled.
After you Gerber Export the part you can check it by opening drill.txt.
The first group shows the drill sizes in inch.
The following groups are in drill size groups, which you can count, and even mathematically work out positions for by using the X and Y coordinates.