Your Arlo Mobile SIM card is preactivated and comes with 15 minutes of prepaid service. You do not need to activate your SIM card.
However, you do need to pick an Arlo subscription plan and an Arlo Mobile service plan while setting up your Arlo Go camera. If you exit the setup process without picking an Arlo Mobile service plan, your Arlo Go camera goes offline after you use your 15 minutes of prepaid service. You can add more minutes to your Arlo Go service plan at any time by going to Settings > Subscription in the Android or web version of the Arlo app.
Arlo sends you email notifications when you have 25%, 10%, and 0% of your prepaid minutes left.
For more information, see the following knowledge base articles: