fix: referee cannot downgrade plan from Lite to Starter (edge case)

When I use a referral link to sign up for Storacha and choose lite, I can't downgrade to Starter and am given this error:

<img width="486" alt="error" src="https://github.com/user-attachments/assets/f3847718-80b9-4c11-bc17-9fd5d4184fb0" />
