After you use a Product ID for one product in App Store Connect, it can’t be used again across any of your apps, even if the product is deleted.

We recommend using a consistent naming scheme across all of your product identifiers to avoid reusing them such as:

<app>_<price>_<duration>_<intro duration><intro price>

• app: Some prefix that will be unique to your app, since the same product Id cannot but used in any future apps you create.
• price: The price you plan to charge for the product in your default currency.
• duration: The duration of the normal subscription period.
• intro duration: The duration of the introductory period, if any.
• intro price: The price of the introductory period in your default currency, if any.

In this case, I want to set up a yearly subscription with a one week trial for $39.99 USD. Using this format I've set my product identifier as:

rc_3999_1y_1w0