You might want to look at this on the quirm.net site:
eShop users – important news
Posted on Friday, May 14th, 2010 at 5:08 pm in
* Plugins,
* WordPress
If you upgraded to 5.2.1 I unfortunately introduced a small error that stops people from being able to checkout. So please upgrade to 5.2.2 as soon as possible.
I apologise for the inconvenience.
