set up RTT phone calls, you can choose to make an RTT call.
Contacts: Select a contact, move your pointer over a phone number, then click the Phone button .
Calendar: Open an event, look for an underlined blue phone number in the event details, click the number, then click Call.
Reminders: Open the reminders list, click an underlined blue phone number, then click Call.
Find My: Open the People list, then select a name. Click the Info button appears next to those people you can’t call.
On your Mac, when a notification appears in the top-right corner of the screen, do one of the following in the notification:
Accept an incoming call: Click Accept.
If the person calling you has set up RTT for the call and you want to answer it that way, click RTT.
Decline a call: Click Decline.
Tip: If the call came from someone you don’t want to receive calls from, you can next to Decline, then choose how long you want to wait to receive a reminder. When the time comes, you receive a notification—click it to view the reminder, then click the link in the reminder to start the call.
If your Mac has a Apple Support article: If FaceTime isn’t working on your Mac