Hello there bbuchanan.
It seems you are having issues with making FaceTime calls on your iMac 27" computer. The following Knowledge Base article offers up some great information for troubleshooting:
FaceTime for Mac: Troubleshooting FaceTime
https://support.apple.com/en-us/HT203585
You can make FaceTime calls using the FaceTime app. You can call FaceTime users whose contact information is in Contacts. You can add contacts and edit contact information in either FaceTime or Contacts. To place a video call, you may use a phone number or email address.
If you encounter issues making or receiving FaceTime calls, try the following:
- Verify that FaceTime is enabled in FaceTime > Preferences.
If the issue persists, or if you see the message "Waiting for Activation", try toggling FaceTime off and then on.
- Verify that the Date, Time, and Time Zone are set correctly:
- From the Apple () menu, choose System Preferences > Date & Time > Date & Time.
- Enable "Set Automatically".
- Click the Time Zone tab and confirm the closest city is correct.
- Verify that both parties are connected to an active broadband Internet connection.
- Verify the phone number or email address being used is the correct one activated for FaceTime.
You can verify that you are using a valid Apple ID at appleid.apple.com. You can also create an Apple ID or reset your password from this website.
- Verify that both parties have installed the latest software updates for their Mac and/or device. See:
Thanks for reaching out to Apple Support Communities.
Kind Regards.