Why is the Renewal price different from the initial payment?

There are various plans available on the MadMuscles website.

Frequently discounted introductory periods are available to our users. Unless cancelled, when this time period expires, the introductory period is followed by a full membership with a standard price. Subscriptions should be cancelled at least 24 hours before your next billing date if you do not wish to continue. It is essential for us to provide special intro rates so that users can test out the app and its features. 

You will also get information about the planned date of renewal. Please pay attention to it because, since this date, you will be charged the monthly subscription amount.

You can check the renewal price and date by following the instructions in this article.