I have now enabled the credit system. Each user participating in the test should have received 14 credits.
Each synthesizer is free to play as default, the credit amount required to play a single session (30 min) can be set in the “My synths” view. Credit transactions can now be seen in the “My profile” view. There are two different credit types, session and owner credits. Session credits can be used to play the synthesizers and owner credits are received when other people play your synthesizers. The owner credits can be transferred to session credits.
If you notice any bugs about the credit system (or otherwise), please report them in the feedback-category.