Hello! It's great that you want to have your phone unlocked so you can use it with other networks. However, I must clarify that unlocking a phone is a process that involves specific steps and sometimes requires a unique unlock code provided by the original network carrier. In the case of your ZTE A71 5G locked to the Optus network in Australia, you may need to contact Optus directly to request an unlock code.
If you're unable to obtain the unlock code from Optus, you may consider using third-party services that specialize in phone unlocking. These services may require a fee for the unlock code, which you can often pay through methods like PayPal or credit/debit cards.
Before proceeding with any unlocking services, ensure to research and choose a reputable provider to avoid any issues with your device in the future. If you have any more questions or need further assistance, feel free to ask!