Thank you very much for trying the plugin, and sorry to hear it doesn't work for you. Hopefully we can fix it, so that you can still "enjoy" the plugin and use this to monetize your site.
Just to clarify:
1. When you become a publisher you can select your currency in your settings. You can also update it later in "my account" > "Settings". Please note: If buyers have a different currency, they will see the price in their own currency (as well as the publisher currency).
2. For developers we have created the sandbox environment. This helps them doing (extensive) tests when they want to create their own functionality based on the Cleeng platform. However, we very recently have updated the upper boundary from 0.99 to 19.99 for the production site, and likely the sandbox environment hasn't been updated since. We will ensure the issue is fixed on sandbox asap. Sorry for the inconvenience.
3. You mention that the login section on sandbox is not working. Can you be more explicit? What might be good to know is that accounts, purchases and content references are NOT copied in between SANDBOX and PRODUCTION. Meaning you have to create a separate account on sandbox. Let me know if that might have caused the issue or that there is something else you encountered.
thanks for your feedback; and hopefully you are willing to give it another try!