You missed part of it...I was reading more of the fine print. The $10.00 savings is for the first year. It says you "may need to take action to continue the $10/mo discount", then points you to another section of fine print which does not spell out anything you can do to keep the $10.00 discount. Shady bastards!
You start by looking at the T-Mobile agreement:
YouTube TV: Redeem by June 30, 2021. After trial pay $54.99/mo. including $10/mo. off for 12 months Cancel anytime. Must be 18 years or over. YouTube TV not available in Puerto Rico, Guam, or US Virgin Islands. Excludes T-Mobile for Business customers. Full terms: YouTube TV - FAQs. After 12 months users may need to take action to continue the $10/mo discount on qualifying streaming services.
Standard Free Trial + $10 off/month for 12 months for T-Mobile Wireless and Internet CustomerssPromotion open to participants subscribing to T-Mobile Wireless or Internet service from April 06, 2021 - June 30, 2021 and must be redeemed by July 31, 2021. Offer redeemable where YouTube TV is available. Standard free trial available for new YouTube TV subscribers who have never participated in a YouTube TV trial. Discount offer available for all T-Mobile customers, regardless if user has enrolled in YouTube TV in the past. Local channel availability may vary. Promotional value of subscription(s) nontransferable, not for resale, and not redeemable for cash. If you are currently subscribed to YouTube TV you will need to cancel your subscription to take advantage of this offer. Valid payment form req’d at sign-up. User will receive standard free trial, if eligible, and then receive $10 discount per month for 12 months (currently $54.99) before being charged price of $64.99/month or then current monthly subscription price. Cancel any time before standard free trial is over at no charge. No refunds for partial billing periods are available. Must be 18 years or older. Google account required. YouTube reserves the right to change or cancel the offer at any time.
After 12 months T-Mobile reserves the right to require billing on your T-Mobile bill to continue $10/mo. discount on qualifying streaming services, consumer action may be required