In the credit history section, you can review every credit log.
Buying a credit package log
After buying a credit package it will be added to your balance and shown in your credit history log.
Launch a target audience log
When a target audience is launched, the required amount of credits will be bound until the target audience receives all its completes. If you pause the target audience, the bound credits will be unbound until you re-launch it again. After the completion of the review process, the target audience will be taken to "live" and the bound credits will be charged for each collected response.
Let's say that you want to launch your first target audience to get 15 testers and your balance is 250 credits. This target audience costs 15 credits (based on the attributes and the study settings you have set). Those 15 credits will be bound while the target audience is live. Now your balance is 235 credits. You want to make a change and get 10 testers instead of 15. So you pause it to edit the target settings. The 15 credits are unbound and return to your balance. You make the change from 15 users to 10 users and re-launch the study. The target audience costs 10 credits and your balance is 240 credits. In the image below you can see the log of our example.