Ordering PCBs online (using Gerber files): A walkthrough. --- featuring the fab "JLCPCB"

I have made about 450 orders to JLCPCB over the years.
Very rarely have a problem.
Best price and shipping isnt too bad.
For small orders I use cheapest shipping but for medium to large orders I use Fedex which is quicker and almost the same price as cheapest.

I wrote my own PCBCAD software and adjusted it to provide all the correct file extensions that JLCPCB prefer.
Makes ordering much simpler.
 
In spite of Mark J's excellent intro to JLCPCB ordering I find myself stuck.
After uploading the gerber I place the order, the Calculated Price updates and, the "save to cart" bar turns light blue. The cart does not update and that is it.
I am using win8pro64 and win10home64 An help is appreciated! E