Calendar Month Pricing / Periodic Month Pricing

Hello,

After processing the data I received from another source in my new application, I will offer it for sale as a monthly subscription.

However, pricing for my data source is based on calendar month, but subscription flows start from the purchase date and I could not find such a subscription flow in the store kit.

How can I draw this flow in a way that doesn't violate app store rules regarding pricing?

Calendar Month Pricing / Periodic Month Pricing
 
 
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