Stripe Subscription Anchor Configuration on current and future subscriptions

I am Riccardo Girardi, from Italy, and I am the owner of a SaaS.

Through the Stripe dashboard I set the subscriptions of my clients.

I have some customers on whom I would like the charge to always go ON THE LAST DAY OF THE MONTH (I bill them for the month just passed).

Others on whom I would like the charge to always go ON THE FIRST DAY OF THE MONTH (I bill them for the service for the incoming month)

Because of February 28, 30 on some monthes and 31 on some others, I unfortunately find that the subscription charge dates get out of sync.

I contacted Stripe Support and they told me about the possibility of acting on “billing_cycle_anchor_config” but I have no programming skills and that is the reason I am here.

What do I need?

For me to set up two API calls.

(a) API call update subscription. In which once provided

- Client ID
- Subscription ID
- Day of the month in which I want to anchor the payment

the subscription collection date is changed.

(b) API call create subscription. In which once provided
- Client ID
- Product ID
- ID Price
-Day of the month I want to anchor the payment.

the subscription is created for me as a request.

I probably wasn't very “technical” but I hope you caught my needs.

Can someone help me with that?