In the Free Tier, you are allowed a maximum of 3 concurrent connections per user.
This is a limitation we place in order to ensure stable service for all our free tier users. It appears that your project requires more connections, and hence, you are facing this issue.
To resolve this, you would need to upgrade to a higher plan which allows more concurrent connections. Our Basic Plan would be an ideal next step.
With the Basic Plan, you will have a higher number of concurrent connections, improved performance, and additional benefits. For more information about our plans, please visit our pricing page.