Solution:

We can do this by saving a Payment Token to the Contact. To save a Payment Token, you can do one of the below.

A. Scenario one: The client enters their credit card information

1. You can Grant the Contact Portal Access.

2. The Contact can then log in to their Portal and update their Payment Settings.

3. Or once you create the Sales Order make sure to check the Online Payment checkbox.

4. When you send the Quotation, the customer can then Sign, Pay, and save the Payment Token. 

B. Scenario two: You enter the client's credit card information.

1. Grant Contact Portal Access.

2. Go to Settings => Manage Users => Filter for Portal Users => Click on Action => Change Password.

3. Log in as the customer, Manage Payment Methods, and input the customer's credit card.

Process:

1. If the Customer paid their Subscription on their Portal and saved the Payment Token, the Payment Token will be added automatically to the Subscription and it will be billed each period automatically using one of the Payment Providers.

2. If you saved the Payment Token manually on the customer's Portal then you can add the Payment Token manually to the Subscription (or pay it from their Portal.)

3. After this each period Odoo will create the Invoice and Register the Payment using the saved Payment Token automatically.

Thanks​