After purchasing your plan go to proxy dashboard

select plan and click USER button as highlighted below

After doing so your proxies will come in the following format

IP:PORT:USER:PASS

Do not click the button again, or it will change the user/pass. Click only once and copy your new proxy list. When in user:pass mode, the proxies will work on all devices, you do not and should not authenticate your IP after switching to user:pass mode.