I’m getting Errors

Each plan (package) is limited by number of threads (simultaneous connections).

If you have package with 40 threads and your software use 41 threads you will see errors and proxies will not work. The same apply if you use proxies on two servers – total number of threads can’t be bigger then what is maximum number of threads in your package.

Some softwares use browser to perform automated actions.
Each browser tab consumes around 10 threads because it loads images, javascript, and other elements all together.

With such software tools you need to lower threads inside software and to upgrade to some of bigger packages.