Create a draft credit note

Create a credit note in DRAFT status against an existing invoice. The credit note is not applied to the invoice until you call POST /credit-notes/:id/issue.

Required for refunds, corrections, and post-issuance adjustments — especially in EU/LATAM jurisdictions where simply voiding an invoice is not legally sufficient.

Validates that:

• the invoice exists and belongs to the business
• the invoice is not in DRAFT or VOIDED status
• the credit note total does not exceed the remaining invoice value