Users with an Apple TV+ subscription should be able to get the 20–23% discount on the MLS Season Pass. Verify your active subscriptions. Verify that that the same Apple ID account is used for both services. The $79/$99 is US prices; it will be different for other dollar currencies (e.g. CA: $99/$129). Verify that the system software on your devices is up-to-date. Also try a restart of the iPhone, in case a some information isn’t refreshing as it should.
If you still don’t see it with the correct price, then contact Apple Support for further assistance.
I see the discount on my iPhone, with the strikethrough of the full price?!?