There was no need for me to delete all my certs. Identifying the bad certificate:From you Keychains select LoginFrom Category select CertificatesFind any Apple Certificate that has the blue +Double click on the certificate.Expand the TrustIf it's messed up then the "When using this certificate" is set to "Always Trust" along with the blue +Fixing the bad certificate:Just set it to "Use System Defaults" and close it.You'll get a pop up. Type in your password to update settings.Close KeyChain. Go back to your project, clean and run. Problem should have gone away.If that didn't work then go back to Keychain and just double check and see if there are any other Apple certificates that are set to Always Trust and repeat the process.

The accepted answer is misleading!If all you want is too group notifications on the device's notificationCenter then you don't need `NotificationContentExtension`!Just pass in `thread-id` in your payload. The only problem is that you have to wait a bit so the iOS renders the notifications into groups. After it renders the first time, then it starts to work. This seems like a bug to me!The following quote on docs is about something else: >The system calls this method to deliver notifications to your Notification Content app extension. Use this method to configure the contents of your view controller or to incorporate content from a new notification. This method may be called multiple times while your view controller is visible. Specifically, it is called again when a new notification arrives whose threadIdentifier value matches the thread identifier of the notification already being displayed. The method is called on the main thread of your extension. Think of iMessage. You get a message from your friend. You Long press the notification. It will open a pop where you can chat from within the contentExtension If your friend sends more messages, then your content-extension's ` didReceiveNotification: docs again because the payload will be of the same `threadi-d`. It gets called so you can update the conversation. ☝has nothing to do with grouping. Grouping and getting continous callbacks to your contentExtension for a single thread-id are just two separate use cases of using `thread-id`!