diff --git a/lang/sl.json b/lang/sl.json
index 141b379d..11a1ce3c 100644
--- a/lang/sl.json
+++ b/lang/sl.json
@@ -1854,6 +1854,7 @@
     "credit_quantity_invalid": "Enter a valid quantity greater than zero for every selected line.",
     "credit_note_cannot_be_cloned": "A credit note cannot be cloned.",
     "credit_note_cannot_be_converted_to_estimate": "A credit note cannot be converted to an estimate.",
+    "invoice_must_be_settled_before_completion": "Record a payment or create a credit note before completing this invoice.",
     "payment_amount_exceeds_invoice_due_amount": "The payment is more than the invoice's outstanding balance.",
     "payment_number_used": "Številka plačila je bila že uporabljena.",
     "name_already_taken": "Ime je že zasedeno.",