Remove flex discount code from a subscription

### Is there an existing issue for this?

- [x] I have searched the existing issues

### What's missing?

I'm testing this feature and I managed to add a discount code to the subscription, but when I tried to remove it, it didn't work, even though the request returned with a success status. Is it only possible to remove it after the subscription is renewed?
The response doesn't return the offerId in the JSON object. This also happens when updating the subscription.

Start by reproducing the subscription discount-code add and removal requests, then inspect the subscription update response described in the issue. Confirm the expected behavior for removing the discount and ensure the response includes the offerId for both operations.

Written by the indexing model from the issue text.