@Cameron_1961 - are you creating a new public mobile account? If so, you need to download the Public Mobile app to create a new account. What issue are you having?
Maybe they can help here, they are closed soon, click this link to use the: Public Mobile Online Activation Assistance
OR, are you trying to change your physical sim card number on your existing account. See "How To Change Your SIM Number" in this Help Article: https://www.publicmobile.ca/en/on/get-help/articles/change-sim-number
edit, typo
