Dear Customer,
Limit can be done by assigning the credits to the users, let's say you need to assign 500 credits; please follow the below steps;

Click on Billing Section
Click on Share Credits option
Enter the user's email & the credit you want to share to the particular user.

Kindly let us know if you're able to achieve so or drop us an email to support@xemailverify.com or create a ticket by browsing the link: https://support.xemailverify.com/portal/en/home

Thank You!