I am having the same issue. Did you contact customer service? I am going to try to chat with an agent regarding this.
It would be great to know how we can utilize the mailed coupon.
@beardsleyf I am so sorry to hear that you are having trouble activating your coupon. You do not require an activation code. For your convenience, I have listed the steps here to get that coupon activated. Let me know if you experience any issues.
Click the Activate Your Coupon button in the email that was sent to you or, if you received a letter in the mail, visit the Xfinity microsite at https://comca.st/3cudgda.
Click the Sign In button, then sign in using your Xfinity ID and password.
Click Begin Activation.
Choose how you want to use your coupon.