diff --git a/doc/invoice.go b/doc/invoice.go
index 640e702..bf13168 100644
--- a/doc/invoice.go
+++ b/doc/invoice.go
@@ -122,9 +122,11 @@ func newImporteTotal(inv *bill.Invoice) string {
 	totalWithDiscounts := inv.Totals.Total
 
 	totalTaxes := num.MakeAmount(0, 2)
-	for _, category := range inv.Totals.Taxes.Categories {
-		if !category.Retained {
-			totalTaxes = totalTaxes.Add(category.Amount)
+	if inv.Totals.Taxes != nil {
+		for _, category := range inv.Totals.Taxes.Categories {
+			if !category.Retained {
+				totalTaxes = totalTaxes.Add(category.Amount)
+			}
 		}
 	}
 
@@ -133,9 +135,11 @@ func newImporteTotal(inv *bill.Invoice) string {
 
 func newRetencionSoportada(inv *bill.Invoice) string {
 	totalRetention := num.MakeAmount(0, 2)
-	for _, category := range inv.Totals.Taxes.Categories {
-		if category.Retained {
-			totalRetention = totalRetention.Add(category.Amount)
+	if inv.Totals.Taxes != nil {
+		for _, category := range inv.Totals.Taxes.Categories {
+			if category.Retained {
+				totalRetention = totalRetention.Add(category.Amount)
+			}
 		}
 	}
 
@@ -204,6 +208,9 @@ func newFacturasRectificadasSustituidas(inv *bill.Invoice) *FacturasRectificadas
 }
 
 func hasSurchargedLines(inv *bill.Invoice) bool {
+	if inv.Totals == nil || inv.Totals.Taxes == nil {
+		return false
+	}
 	vat := inv.Totals.Taxes.Category(tax.CategoryVAT)
 	if vat == nil {
 		return false
diff --git a/document.go b/document.go
index 5f1673a..37284e3 100644
--- a/document.go
+++ b/document.go
@@ -27,6 +27,9 @@ func (c *Client) Convert(env *gobl.Envelope) (*doc.TicketBAI, error) {
 	if inv.Supplier.TaxID.Country != l10n.ES.Tax() {
 		return nil, ErrValidation.withMessage("only spanish invoices are supported")
 	}
+	if inv.Totals == nil || inv.Totals.Taxes == nil {
+		return nil, ErrValidation.withMessage("missing taxes")
+	}
 
 	zone := zoneFor(inv)
 	if zone == "" {
diff --git a/test/data/credit-note-es-es-tbai.json b/test/data/credit-note-es-es-tbai.json
index 96fd3f0..b449be6 100644
--- a/test/data/credit-note-es-es-tbai.json
+++ b/test/data/credit-note-es-es-tbai.json
@@ -4,7 +4,7 @@
 		"uuid": "0192237d-4943-72a7-b1d0-51dca3e8bc71",
 		"dig": {
 			"alg": "sha256",
-			"val": "f7165b79e26a6d53e163030b0312e80d15f8af189e0eb51d98864cb06c64e9fc"
+			"val": "c703a148a9395e3a14882d582618fe6503ab4719007715449c752eaf5cc22831"
 		}
 	},
 	"doc": {
@@ -86,7 +86,10 @@
 				"item": {
 					"name": "Development services",
 					"price": "90.00",
-					"unit": "h"
+					"unit": "h",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1800.00",
 				"discounts": [
@@ -110,7 +113,10 @@
 				"quantity": "1",
 				"item": {
 					"name": "Financial service",
-					"price": "10.00"
+					"price": "10.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "10.00",
 				"discounts": [
diff --git a/test/data/invoice-es-es-b2c.json b/test/data/invoice-es-es-b2c.json
index b86f37e..ba1b91e 100644
--- a/test/data/invoice-es-es-b2c.json
+++ b/test/data/invoice-es-es-b2c.json
@@ -4,7 +4,7 @@
 		"uuid": "0192d3c7-2dc5-74cf-b263-5892feb44432",
 		"dig": {
 			"alg": "sha256",
-			"val": "58a808907be339175b8fa53ff5f326f1f074641cfbb653f7f1619763e1f4f2d7"
+			"val": "57cfc9eb9cc3c8b0013b7ad7ff6fc8b0320d9afbeda923eea05c463bd3cc16cd"
 		}
 	},
 	"doc": {
@@ -56,7 +56,10 @@
 				"item": {
 					"name": "Development services",
 					"price": "90.00",
-					"unit": "h"
+					"unit": "h",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1800.00",
 				"discounts": [
@@ -83,7 +86,10 @@
 				"quantity": "1",
 				"item": {
 					"name": "Some merch",
-					"price": "90.00"
+					"price": "90.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "90.00",
 				"taxes": [
@@ -103,7 +109,10 @@
 				"quantity": "1",
 				"item": {
 					"name": "Some essential needs merch",
-					"price": "30.00"
+					"price": "30.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "30.00",
 				"taxes": [
diff --git a/test/data/invoice-es-nl-b2c.json b/test/data/invoice-es-nl-b2c.json
index 4e7c1cc..881a847 100644
--- a/test/data/invoice-es-nl-b2c.json
+++ b/test/data/invoice-es-nl-b2c.json
@@ -4,7 +4,7 @@
 		"uuid": "0192237d-4965-7c4b-914e-3a62f8e074e5",
 		"dig": {
 			"alg": "sha256",
-			"val": "0ab95209a3a9da3f9e4500a39cd9685f142ff86d42e3d143de14042fe6639749"
+			"val": "b796c7ee85d32112c3ce7690f4ba5498eaf196ab9df57ea3a2128fe90247b612"
 		}
 	},
 	"doc": {
@@ -68,7 +68,10 @@
 				"item": {
 					"name": "Development services",
 					"price": "90.00",
-					"unit": "h"
+					"unit": "h",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1800.00",
 				"discounts": [
@@ -96,7 +99,10 @@
 				"quantity": "1",
 				"item": {
 					"name": "Some merch",
-					"price": "90.00"
+					"price": "90.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "90.00",
 				"taxes": [
@@ -117,7 +123,10 @@
 				"quantity": "1",
 				"item": {
 					"name": "Some essential needs merch",
-					"price": "30.00"
+					"price": "30.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "30.00",
 				"taxes": [
diff --git a/test/data/invoice-es-nl-tbai-b2c-explicit.json b/test/data/invoice-es-nl-tbai-b2c-explicit.json
index e96e6e2..231ce6c 100644
--- a/test/data/invoice-es-nl-tbai-b2c-explicit.json
+++ b/test/data/invoice-es-nl-tbai-b2c-explicit.json
@@ -4,7 +4,7 @@
 		"uuid": "0192237d-498e-7273-bc95-6a1daf16cb37",
 		"dig": {
 			"alg": "sha256",
-			"val": "bc1cc3c6887e628c94e42d011041522695a73005a3daf4b0f521b9a297e9e97f"
+			"val": "68b6594f9204664935f572e9fc537e84f680c86a4a325f61ddd646685ffcbde7"
 		}
 	},
 	"doc": {
@@ -65,7 +65,10 @@
 				"item": {
 					"name": "Development services",
 					"price": "90.00",
-					"unit": "h"
+					"unit": "h",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1800.00",
 				"discounts": [
diff --git a/test/data/invoice-es-nl-tbai-exempt.json b/test/data/invoice-es-nl-tbai-exempt.json
index b39f90c..364f6e2 100644
--- a/test/data/invoice-es-nl-tbai-exempt.json
+++ b/test/data/invoice-es-nl-tbai-exempt.json
@@ -4,7 +4,7 @@
 		"uuid": "0192237d-49c2-79a7-8249-4280119d8ade",
 		"dig": {
 			"alg": "sha256",
-			"val": "0294246ded2b071f8c6eb6011251f3bd254726613b5e7402abcbc2c91e96ecd1"
+			"val": "f9db4d04b45e555f37068e2d363c153d0a36e29bbdfd828452a78a92491babec"
 		}
 	},
 	"doc": {
@@ -60,7 +60,10 @@
 				"item": {
 					"name": "Development services",
 					"price": "90.00",
-					"unit": "h"
+					"unit": "h",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1800.00",
 				"discounts": [
diff --git a/test/data/invoice-ss.json b/test/data/invoice-ss.json
index 61cc1cb..e386688 100644
--- a/test/data/invoice-ss.json
+++ b/test/data/invoice-ss.json
@@ -4,7 +4,7 @@
 		"uuid": "0192fbbc-005b-7eea-8973-210ca4c0ffdc",
 		"dig": {
 			"alg": "sha256",
-			"val": "265465a226476105b9339754dd8e8856033fca217b8b6e89a984295de402b4b6"
+			"val": "38e8aef5c956bd0ca7ab99d559bdb13174a3f6af82feab70e1e7242bfe10abe7"
 		}
 	},
 	"doc": {
@@ -74,7 +74,10 @@
 				"quantity": "10",
 				"item": {
 					"name": "Item being purchased",
-					"price": "100.00"
+					"price": "100.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1000.00",
 				"discounts": [
diff --git a/test/data/invoice-vi.json b/test/data/invoice-vi.json
index e3a54a1..faf9409 100644
--- a/test/data/invoice-vi.json
+++ b/test/data/invoice-vi.json
@@ -4,7 +4,7 @@
 		"uuid": "0192fd51-6cd8-73f2-a182-8c4d3901d125",
 		"dig": {
 			"alg": "sha256",
-			"val": "a9fcef2ca22b63043a5c66137a39f8ad2be7db01c42ad94f4c5c80ee060c49b0"
+			"val": "6503a793d90d96cefdfd1652d219a43e44472eb5e8f741d43cf86cb8f984b2ec"
 		}
 	},
 	"doc": {
@@ -74,7 +74,10 @@
 				"quantity": "10",
 				"item": {
 					"name": "Item being purchased",
-					"price": "100.00"
+					"price": "100.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1000.00",
 				"discounts": [
diff --git a/test/data/sample-invoice-export.json b/test/data/sample-invoice-export.json
index c9de11c..1b90c24 100644
--- a/test/data/sample-invoice-export.json
+++ b/test/data/sample-invoice-export.json
@@ -4,7 +4,7 @@
 		"uuid": "0192fbd4-5087-708c-9b31-e8f653ef0c52",
 		"dig": {
 			"alg": "sha256",
-			"val": "27db0398b2f300511bfb0401a576876e5061248930ba31fb4d3bd140bddd5a6f"
+			"val": "963d8171e4ecb8b3c6fa952ce32849d2093fc9f56b9ee35a61741b043bc588d4"
 		}
 	},
 	"doc": {
@@ -71,7 +71,10 @@
 				"quantity": "6",
 				"item": {
 					"name": "Item being purchased",
-					"price": "100.00"
+					"price": "100.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "600.00",
 				"taxes": [
@@ -91,7 +94,10 @@
 				"quantity": "5",
 				"item": {
 					"name": "Another item being purchased",
-					"price": "20.00"
+					"price": "20.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "100.00",
 				"taxes": [
@@ -111,7 +117,10 @@
 				"quantity": "2",
 				"item": {
 					"name": "Service being paid",
-					"price": "150.00"
+					"price": "150.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "300.00",
 				"taxes": [
diff --git a/test/data/sample-invoice-supplier2.json b/test/data/sample-invoice-supplier2.json
index 083e0bd..120b52f 100644
--- a/test/data/sample-invoice-supplier2.json
+++ b/test/data/sample-invoice-supplier2.json
@@ -4,7 +4,7 @@
 		"uuid": "0192fbd4-81b4-75ed-899b-eb4c18a65f1c",
 		"dig": {
 			"alg": "sha256",
-			"val": "177b1a668214b82d634010ca686f671872c4f98865f4c259b88d8025dfbc3aaf"
+			"val": "cff6f81c8bb31fcf3fbed5429b07a2a9fd36d5ba349592ec83d70f63399be1c5"
 		}
 	},
 	"doc": {
@@ -74,7 +74,10 @@
 				"quantity": "15",
 				"item": {
 					"name": "Item being purchased",
-					"price": "90.00"
+					"price": "90.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1350.00",
 				"discounts": [
diff --git a/test/data/sample-invoice.json b/test/data/sample-invoice.json
index 7b3de71..3d369aa 100644
--- a/test/data/sample-invoice.json
+++ b/test/data/sample-invoice.json
@@ -4,7 +4,7 @@
 		"uuid": "0192fbd4-a54b-7d7a-be6e-258ea15f17a2",
 		"dig": {
 			"alg": "sha256",
-			"val": "2900e06e5224e2b3c6bf004d036ee3356d3f2a4220fd3deaa80ae871915670b7"
+			"val": "3d0c71a198b2d0bcf3c07dede6e291c2c552577d7b20c13339fcbc3b77d38ab2"
 		}
 	},
 	"doc": {
@@ -74,7 +74,10 @@
 				"quantity": "10",
 				"item": {
 					"name": "Item being purchased",
-					"price": "100.00"
+					"price": "100.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1000.00",
 				"discounts": [
diff --git a/test/data/sample-invoice2.json b/test/data/sample-invoice2.json
index ca35e79..3a97c14 100644
--- a/test/data/sample-invoice2.json
+++ b/test/data/sample-invoice2.json
@@ -4,7 +4,7 @@
 		"uuid": "0192fbd5-3b54-7735-a8de-2e4f13219f68",
 		"dig": {
 			"alg": "sha256",
-			"val": "61ef29f84ae8f5fe2e0366a0a0dd3582c75dcd46884335619a9d1129343bfa56"
+			"val": "f598c765c4aa997dff2f37c711415164a459dabd7805d39fcd0321b87bc21cd0"
 		}
 	},
 	"doc": {
@@ -74,7 +74,10 @@
 				"quantity": "15",
 				"item": {
 					"name": "Item being purchased",
-					"price": "90.00"
+					"price": "90.00",
+					"ext": {
+						"es-tbai-product": "services"
+					}
 				},
 				"sum": "1350.00",
 				"discounts": [