This documentation should help you with the certification/token generation process to check if you are following the right steps: https://learn.microsoft.com/en-us/azure/notification-hubs/ios-sdk-get-started
While generating the push certificate, try the Production Push Certificate if Developer isn't working as it helps sometimes even if you are using XCode and select the same accordingly in the azure portal while setting up authentication (production or sandbox)
Hope this helps!