[BUG] [Bug/Billing] Multiple Claude Max Gift Cards converted to flat credit instead of stacking duration, resulting in financial loss

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Description

There is a critical backend billing bug between Claude's gifting mechanism and Stripe's subscription management. When a user redeems multiple 1-month gift subscriptions consecutively, the system fails to stack the subscription duration. Instead, it converts them into a flat credit balance and prematurely consumes/voids the remaining prepaid value upon the next billing cycle.

Worse, Anthropic's first-line email support closed my ticket without any actual resolution, claiming it's "not a system issue." I am opening this public issue because this is a clear programmatic defect where international users are losing real money.

Steps to Reproduce

1. Receive three separate 1-Month Claude Max 5x gift subscriptions (Total face value: $300).
2. Redeem all three codes consecutively on a single account.
3. Observe that the system converts the codes into a flat $300 credit balance rather than extending the subscription end-date by 3 months.
4. Upon the monthly billing cycle, Stripe charges $110 (including 10% South Korea VAT) for just 1 month of service.
5. The remaining 2 months of prepaid value ($200) are effectively swallowed, misallocated, or the user is locked out from using the full 3-month term.

Expected Behavior

The gift codes should stack the subscription duration line-item by line-item (e.g., 1 month + 1 month + 1 month = 3 months of continuous access). It should not treat prepaid duration vouchers as a one-time cash balance that breaks Stripe's proration logic.

Environment / Context

• Product: Claude Max 5x Gift Subscription (1-Month x 3)
• Region: South Korea (Billing address subject to 10% VAT)
• Support Status: Official email inquiry was closed by the support agent without a fix.

Additional Request

Since first-line support representatives or automated AI bots do not have the backend authority to modify billing entitlements, I request an Anthropic Engineer or Community Manager to escalate this defect to the Billing Engineering / Stripe Integration Team.

I need my account manually provisioned for the remaining 2 months of Claude Max access that I rightfully paid for.

What Should Happen?

The gift codes should stack the subscription duration line-item by line-item (e.g., 1 month + 1 month + 1 month = 3 months of continuous access). It should not treat prepaid duration vouchers as a one-time cash balance that breaks Stripe's proration logic.

Error Messages/Logs

Steps to Reproduce

1. Receive three separate 1-Month Claude Max 5x gift subscriptions (Total face value: $300).
2. Redeem all three codes consecutively on a single account.
3. Observe that the system converts the codes into a flat $300 credit balance rather than extending the subscription end-date by 3 months.
4. Upon the monthly billing cycle, Stripe charges $110 (including 10% South Korea VAT) for just 1 month of service.
5. The remaining balance becomes $190, which is insufficient for the next 2 months of service ($220 required with VAT), preventing me from using the full 3-month term.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.212

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_