This is how a backconnect package works. There is a pool of proxies, thousands of them. There are gateway ip:ports (from a single one to several thousands in our case). These ip:ports connect pool to the Internet. You input the IP:Port into your software/browser, and the Internet sees random IPs from the pool.
These IPs get assigned to your port and get swapped (replaced) over a time period. We can set up a certain time period or we can set up instant swap (meaning IP will change every new request).