Facetime activation error

Hello Sahilhossain,

We'd like to assist you with a few steps that can assist you with getting your phone number activated in FaceTime:

1. "Make sure that you're using the latest software for your Mac or iOS device. 
2. Make sure that you correctly followed the iPhone steps to set up your phone number. You should be using the same Apple ID on all of your devices.
3. In the “You can be reached” section of Messages and FaceTime settings, make sure that there are checkmarks beside your phone number and Apple ID:
4. 

If your phone number is unchecked and you can't select it, or you have some other issue, follow these steps:

1. On your Mac:

• In Messages, choose Messages > Settings, then click iMessage. Click Sign Out.
• In FaceTime, choose FaceTime > Settings, then click General. Click Sign Out.

1. On your iPhone, iPad, and iPod touch:

• Go to Settings > Messages > Send & Receive. Tap your Apple ID, then tap Sign Out.
• Go to Settings > FaceTime. Tap your Apple ID, then tap Sign Out.

1. On your iPhone:

• Go back to Settings > Messages and make sure that iMessage is turned on.
• Tap Send & Receive, then choose “Use your Apple ID for iMessage” and sign in with your Apple ID.

1. Using the same Apple ID, sign back in to Messages and FaceTime on your other devices. 

If you still need help, change your Apple ID password and repeat the setup steps."

More details here: Add or remove your phone number in Messages or FaceTime

If you're still unable to activate your phone number, follow the link to connect with Apple directly. They'll be able to assist you further: Get Support

Best regards.