[BUG] Billing: $50 promotional credit never applied — card charged while credit remains full

Bug Description

I'm on the Claude Max 5x plan ($100/month). I have been paying for extra usage via credit card. When the $50 Opus 4.6 promotional credit was offered, I claimed it. However, the $50 credit has NEVER been applied to any of my extra usage charges. My credit card continues to be charged for all extra usage while the $50 promotional credit sits untouched in my account.

Steps to Reproduce

1. Active Claude Max 5x plan ($100/month)
2. Extra Usage enabled — paying extra usage charges via credit card
3. Claimed $50 Opus 4.6 promotional credit
4. Continued using Claude Code
5. Card continues to be charged for extra usage
6. $50 promotional credit remains at full balance — never deducted

Expected Behavior

The $50 promotional credit should be applied to extra usage charges first, before charging the credit card.

Actual Behavior

• $50 promotional credit: remains full, never applied
• Credit card: continues to be charged for all extra usage after the promotion
• The credit appears to be purely decorative — it exists but is never used

Environment

• Plan: Claude Max 5x ($100/month)
• Date: February 2026
• Platform: Windows 11

Related Issues

• #23674 — $50 credits disappeared after renewal
• #25586 — $50 promotional credit disappeared after renewal
• #24727 — Usage tracking mismatch between Claude Code and dashboard