diff --git a/eu_einvoice/european_e_invoice/custom/sales_invoice.py b/eu_einvoice/european_e_invoice/custom/sales_invoice.py
index 478fe59..c7ca176 100644
--- a/eu_einvoice/european_e_invoice/custom/sales_invoice.py
+++ b/eu_einvoice/european_e_invoice/custom/sales_invoice.py
@@ -384,7 +384,7 @@ def _add_line_item(self, item: SalesInvoiceItem):
 					("Tax Category", self.invoice.tax_category),
 					("Sales Taxes and Charges Template", self.invoice.taxes_and_charges),
 				]
-			)
+			).upper()
 
 		li.settlement.monetary_summation.total_amount = item.amount
 		self.doc.trade.items.add(li)
@@ -515,7 +515,7 @@ def _add_empty_tax(self):
 				("Tax Category", self.invoice.tax_category),
 				("Sales Taxes and Charges Template", self.invoice.taxes_and_charges),
 			]
-		)
+		).upper()
 		self.doc.trade.settlement.trade_tax.add(trade_tax)
 
 	def _add_payment_terms(self):