Additional options: if you bought the ticket without but you want

If I buy a ticket without "Additional Option" and after a while, I want to buy it I cannot.
Please allow the customer to buy after purchasing the ticket an additional option.

Why do I want to buy an additional option after I bought the ticket?

- Because the additional option was not available when I bought the ticket (e.g. Early Bird)
- I was thinking I don't need it