If you have more than one course on your teachable, it will be necessary to define which one to use for your specific product during the product creation.

Log in to your teachable account, navigate to course and choose the course you want to connect.

Click pricing,

From the pricing page you should be able to copy your product ID

Paste into your product ID.

If you only have one course in your teachable that you added, its ID in connections, you shall leave it blank.