diff --git a/db/changes/240401/02-invoiceOutConfig_refLen.sql b/db/changes/240401/02-invoiceOutConfig_refLen.sql
new file mode 100644
index 000000000..8b91889f2
--- /dev/null
+++ b/db/changes/240401/02-invoiceOutConfig_refLen.sql
@@ -0,0 +1,2 @@
+ALTER TABLE vn.invoiceOutConfig
+	ADD IF NOT EXISTS refLen TINYINT UNSIGNED DEFAULT 5 NOT NULL COMMENT 'Invoice reference identifier length';
diff --git a/db/changes/240401/00-fixInvoiceOutBeforeInsert.sql b/db/changes/240401/03-fixInvoiceOutBeforeInsert.sql
similarity index 51%
rename from db/changes/240401/00-fixInvoiceOutBeforeInsert.sql
rename to db/changes/240401/03-fixInvoiceOutBeforeInsert.sql
index 10e8d6356..0081c8803 100644
--- a/db/changes/240401/00-fixInvoiceOutBeforeInsert.sql
+++ b/db/changes/240401/03-fixInvoiceOutBeforeInsert.sql
@@ -4,17 +4,20 @@ CREATE OR REPLACE DEFINER=`root`@`localhost` TRIGGER `vn`.`invoiceOut_beforeInse
 	FOR EACH ROW
 BEGIN
 /**
+ * Generates the next reference for the invoice serial. There cannot be gaps
+ * between identifiers of the same serial!
+ *
  * Reference format:
- *  - 0: Serial [A-Z]
- *  - 1: Sage company id
- *  - 2-3: Last two digits of issued year
- *  - 4-8: Autoincrement identifier
- **/
-	DECLARE vNewRef INT DEFAULT 0;
-	DECLARE vCompanyCode INT;
+ *  {0} Invoice serial
+ *  {1} The company code
+ *  {2-3} Last two digits of issue year
+ *  {4-$} Autoincrement identifier
+ */
+	DECLARE vRef INT DEFAULT 0;
+	DECLARE vRefLen INT;
+	DECLARE vRefPrefix VARCHAR(255);
 	DECLARE vLastRef VARCHAR(255);
-	DECLARE vRefStr VARCHAR(255);
-	DECLARE vRefLen INT DEFAULT 5;
+	DECLARE vCompanyCode INT;
 	DECLARE vYearLen INT DEFAULT 2;
 	DECLARE vPrefixLen INT;
 
@@ -23,36 +26,34 @@ BEGIN
 		WHERE id = NEW.companyFk;
 
 	IF vCompanyCode IS NULL THEN
-		CALL util.throw('sageCompanyNotDefined');
+		CALL util.throw('companyCodeNotDefined');
 	END IF;
 
 	SELECT MAX(i.ref) INTO vLastRef
 		FROM invoiceOut i
 		WHERE i.serial = NEW.serial
-			AND i.issued BETWEEN util.firstDayOfYear(NEW.issued) AND util.dayEnd(util.lastDayOfYear(NEW.issued))
+			AND i.issued BETWEEN util.firstDayOfYear(NEW.issued) AND util.lastDayOfYear(NEW.issued)
 			AND i.companyFk = NEW.companyFk;
 
 	IF vLastRef IS NOT NULL THEN
 		SET vPrefixLen = LENGTH(NEW.serial) + LENGTH(vCompanyCode) + vYearLen;
 		SET vRefLen = LENGTH(vLastRef) - vPrefixLen;
-		SET vRefStr = SUBSTRING(vLastRef, vPrefixLen + 1);
-		SET vNewRef = vRefStr + 1;
-
-		IF LENGTH(vNewRef) > vRefLen THEN
-			CALL util.throw('refLenExceeded');
-		END IF;
-
-		SET NEW.ref = CONCAT(
-			SUBSTRING(vLastRef, 1, vPrefixLen),
-			LPAD(vNewRef, LENGTH(vRefStr), '0')
-		);
+		SET vRefPrefix = LEFT(vLastRef, vPrefixLen);
+		SET vRef = RIGHT(vLastRef, vRefLen);
 	ELSE
-		SET NEW.ref = CONCAT(
+		SELECT refLen INTO vRefLen FROM invoiceOutConfig;
+		SET vRefPrefix = CONCAT(
 			NEW.serial,
 			vCompanyCode,
-			RIGHT(YEAR(NEW.issued), vYearLen),
-			LPAD(1, vRefLen, '0')
+			RIGHT(YEAR(NEW.issued), vYearLen)
 		);
 	END IF;
+
+	SET vRef = vRef + 1;
+	IF LENGTH(vRef) > vRefLen THEN
+		CALL util.throw('refIdLenExceeded');
+	END IF;
+
+	SET NEW.ref = CONCAT(vRefPrefix, LPAD(vRef, vRefLen, '0'));
 END$$
 DELIMITER ;
diff --git a/db/dump/fixtures.sql b/db/dump/fixtures.sql
index 923872f8c..b243692bb 100644
--- a/db/dump/fixtures.sql
+++ b/db/dump/fixtures.sql
@@ -600,6 +600,9 @@ INSERT INTO `vn`.`taxArea` (`code`, `claveOperacionFactura`, `CodigoTransaccion`
         ('NATIONAL', 0, 1),
         ('WORLD',    2, 15);
 
+INSERT INTO vn.invoiceOutConfig
+    SET parallelism = 8;
+
 INSERT INTO `vn`.`invoiceOutSerial` (`code`, `description`, `isTaxed`, `taxAreaFk`, `isCEE`, `type`)
     VALUES
         ('A', 'Global nacional',            1, 'NATIONAL',  0,  'global'),
@@ -623,9 +626,6 @@ UPDATE `vn`.`invoiceOut` SET ref = 'T3333333' WHERE id = 3;
 UPDATE `vn`.`invoiceOut` SET ref = 'T4444444' WHERE id = 4;
 UPDATE `vn`.`invoiceOut` SET ref = 'A1111111' WHERE id = 5;
 
-INSERT INTO vn.invoiceOutConfig
-    SET parallelism = 8;
-
 INSERT INTO `vn`.`invoiceOutTax` (`invoiceOutFk`, `taxableBase`, `vat`, `pgcFk`)
     VALUES
         (1, 895.76, 89.58,  4722000010),