AppleTV+ won't play in Safari on my MacBook

Thank you for the additional information.

Join Apple TV+ - Apple Support

6. Start watching

*When you sign in to tv.apple.com for the first time, you might be asked to add or verify a credit card to ensure the account holder has authorized viewing on the web.

This request for a card number is legitimate, and is not used for payment, but for user verification. The details that you enter should match the payment method that Apple already has on file for your Apple ID account.

Change, add, or remove Apple ID payment methods - Apple Support

Other users have indicated that a matching debit card would work just as well.

Safari should be able to access Apple TV+ through the site tv.apple.com. Remember to sign in to the site, using the button in the top-right corner, using the Apple ID account that has the subscription.

What is your version macOS on your notebook?