This article explains how to find the subscription ID for your Microsoft 365 subscriptions.
Log into your Microsoft 365 account. Go to the Admin Center.
Go to Billing > Your Products. Select the desired product.
Locate and copy the subscription ID from the page url.
See Find the Subscription ID of your Microsoft products (Dynamics 365 Customer Engagement Plan) from Nishant Rana's Weblog for more information.