Once you have purchased Residential Proxies, you can create proxy traffic limits by logging into the Oxylabs dashboard, where you will have to follow a few steps:
Select Usage Limits within the menu;
Click Create rule;
Select Residential Proxies as the product;
Choose the proxy users that you want to limit;
Pick the period for limits (daily, monthly, or lifetime);
Set the traffic limit;
Click the Create limit rule to save your settings.
Furthermore, you have the flexibility to determine the course of action when the limit is reached. While the default setting will do nothing, you have the option to receive email notifications and/or disable the proxy user.
See this visual guide on how to set up proxy traffic limits: