The document lifecycle

create business (once per end user)
   └─ create draft ──> PATCH / DELETE freely (a draft is a "קובץ זמני", not a tax document)
         └─ issue ──> IMMUTABLE forever. Number assigned. PDF rendered + digitally signed.
               ├─ prints: origin (מקור): downloadable ONCE ever; then copies (העתק)
               └─ corrections: ONLY by issuing a credit note (or negative receipt)

Two rules Israeli law imposes, which the API enforces:

Issued documents can never be edited or deleted, not by you and not by us (blocked at the database engine). Mistakes are corrected by issuing a credit note (חשבונית מס זיכוי) linked to the original, or for receipts a negative receipt. Plan your UX accordingly: confirm before issue.
The origin (מקור) is delivered exactly once (הוראה 18(ב)2). The first prints call with kind: "origin" returns the origin PDF and permanently consumes it; every later download must use kind: "copy" and returns a PDF watermarked "העתק" (copy). Deliver the origin PDF straight to the end customer. Recommended: use kind: "auto", which serves the origin on the first ever print and copies forever after, so a repeat download button never errors; the X-Print-Variant response header says which variant you got.

Document types

Code	Name	When	Needs lines	Needs payments	VAT
`300`	חשבונית עסקה (proforma)	A demand for payment before the money arrives. Numbered, immutable and exported like the rest, but not a tax document: it moves no VAT and counts as no income; the receipt or tax invoice that follows it does. No credit note: a wrong one is superseded by a new one	✓	-	shown, not effective
`305`	חשבונית מס (tax invoice)	Billing, payment later	✓	-	✓
`320`	חשבונית מס/קבלה (invoice/receipt)	Billing + payment together, the common case	✓	✓	✓
`330`	חשבונית מס זיכוי (credit note)	Correcting 305/320, issued via the credit-note endpoint and not directly	✓	-	✓
`400`	קבלה (receipt)	Payment received (no VAT invoice)	-	✓	-

Dealer type decides what's allowed: an עוסק פטור ("patur") may issue receipts (400) and proformas (300), no VAT documents. "murshe" (עוסק מורשה), "company" (חברה) and "ngo" (עמותה) may issue all five. Sending a disallowed type returns doc_type_not_allowed. Ask your users their dealer type at onboarding and reflect this in your UI.