Did Tesla ask you to the pay the $820?
No.
Did a real human being that works at Tesla give you that estimate?
No.
You are spreading fake news, and congratulations, your post is now trending on Reddit and will be picked up soon by anti-Tesla websites with the headline:
Rear defrost strips falling off window after 17 mos. Tesla wants $820.
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No one wants $820. It will be covered under warranty. The app just automatically shows an estimate of repair costs. Warranty determines who will pay it. In this case, Tesla will pay the $820.