Proration strategy when the merchant switch to Plan B on the first day of Plan A billing cycle

Question: Subscription Billing Cycle Not Aligning with Documentation
Description:
According to the Shopify documentation on subscription billing, when a merchant upgrades or downgrades their plan, the new billing cycle should retain the currentPeriodEnd of the original plan. However, during my testing, this behavior does not seem to align with the documentation.


The Test Step:

  1. The merchant subscribed to the Basic Plan.
  2. Approximately 14 hours later, the merchant switched to the Professional Plan.

Expected Behavior:
The currentPeriodEnd should remain the same as the original plan, per the documentation.

Actual Behavior:
A new subscription was created with a different currentPeriodEnd, as shown in the screenshots below:


Questions:

  1. Is this behavior expected, or is there a potential issue with the billing implementation?

Looking forward to hearing your insights!

Thank you!