I will call this a straight forward fraud. You won't gain any valid participants. Stay away from this platform and invest your time in promoting your study by yourself.
First off, I'm sorry for our late reply.
I'm also sorry we weren't able to work something out with you before. I do see that we have tried to reach out to you twice via email to find a solution but couldn't get in touch. We have a strong suspicion of what may have caused the issue.
If there's anything we can do for you in the future, your credits are still valid, please reach out to firstname.lastname@example.org and we will make sure you will get quality responses fast in return for your effort!