I had success once by getting the parking ticket officer initial my R4C on the ticket. But I caught up with him down the block. I think that is the only time I had success with parking tickets without an evidence repository. The evidence repository shows that you have the "exclusive original cognizance" of the United States government.
I have always had an evidence repository for parking tickets. I believe once the address was in California, for a parking ticket in a Colorado mountain gambling town called Cripple Creek! I never heard anything more on that so I guess that was good R4C process.
A good evidence repository is great for any R4C. You are threatening a cash cow so if this goes south consider
setting up a LoR, evidence repository and get a
default judgment (signed by you) published in your favor. You can use that for all R4C's and show that you are keeping a record - being the court of record.
Mostly though, if this gets nasty just pay up and learn more about the R4C and LoR process.