The on-screen "Invoice Message" text block IS the invoice `note` field, editable via
PUT /invoices/{id} {"note": "..."} (response {"invoice": {...}}). Verified on the ACG
internal test account (#67741: set/verify/restore).
Billing flow now sets a one-line upsell hint on the invoice note — "Interested in
discounted labor? Ask us about block-rate pricing." — ONLY for customers with no prepaid
block (prepay_hours == 0). Block customers (prepay_hours > 0) get no hint; never clobber
a non-empty note.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Mike Swanson
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