Serbia Invoices (SEF eFaktura national API) MCP server

Issue a Serbia B2B electronic invoice (elektronska faktura) into the national SEF eFaktura system (Ministry of Finance). Builds UBL 2.1 XML in the SRB-CIUS customization (Serbia's CIUS of EN 16931) and uploads it under your own SEF API key. Bring your own credential as a header: x-sef-api-key (the API key you self-generate in the SEF portal under Settings -> API management / Podesavanja -> Upravljanje API). Header x-sef-mode: prod switches to the live rail (default = demo, no fiscal effect). You must supply your own seller identity in the arguments (supplier_pib + supplier_name), because SEF validates that the seller in the XML matches your account. Returns sales_invoice_id (SEF's invoice id) — poll query_invoice with it to learn the status (New/Sent/Approved/Rejected/Cancelled...). Serbian VAT rates: 20 (standard), 10 (reduced), 0 (zero-rated). Amounts are in RSD (Serbian dinar). Set send_to_cir=true when the buyer is a budget / public-sector user (registration in the Central Invoice Register / CRF is then mandatory).

Check the SEF status of a sales invoice created by create_invoice, using its sales_invoice_id. Status values (SEF SalesInvoiceStatus): NEW (Nova/New — draft not yet sent); SENDING (in transit); SENT (delivered to the buyer, awaiting their action); SEEN (buyer opened it); APPROVED (buyer accepted — Prihvacena); APPROVED_WITH_RESERVATION (accepted with reservation); REJECTED (buyer rejected — Odbijena); CANCELLED (seller cancelled — Otkazana); STORNO (reversed by a storno document); MISTAKE (marked as an error); OVERDUE (payment past due); REMINDED (a reminder was sent); DELETED. Safe to call anytime.

Cancel (Otkazivanje) a Serbia sales invoice you sent, using its sales_invoice_id and a mandatory reason (cancel_comment). This is the seller cancelling their own Sent invoice before the buyer accepts or rejects it; once the buyer has Approved it, cancellation is no longer possible and a storno (credit) document is required instead (storno is out of scope in v1 — honest limit). Returns the SEF response. Irreversible.