diff --git a/src/models.py b/src/models.py
index c8e1657..955c491 100644
--- a/src/models.py
+++ b/src/models.py
@@ -15,14 +15,11 @@ class Currency(str, Enum):
     GBP = "GBP"
     CHF = "CHF"
 
+    def __str__(self):
+        return self.value
 
-class AmountType(str, Enum):
-    DBIT = "DBIT"
-    CRDT = "CRDT"
-
-    @property
-    def sign(self) -> int:
-        return -1 if self == self.DBIT else +1
+    def __repr__(self):
+        return f"Currency.{self.name}"
 
 
 class B4wExport(BaseModel):
@@ -32,17 +29,28 @@ class B4wExport(BaseModel):
     date_valid: date = Field(alias="ValDt")
     amount: Decimal = Field(alias="Amt")
     amount_currency: Currency = Field(alias="AmtCcy")
-    amount_type: AmountType = Field(alias="CdtDbtInd")
-    reference: str = Field(alias = "RmtInf")
-    other_name: str = Field(alias = "RmtdNm")
-    other_iban: str = Field(alias = "RmtdAcctIBAN")
-    category: Category | None = Field(alias = "Category")
-    notes: str = Field(alias = "Notes")
-
+    sign: int = Field(alias="CdtDbtInd")
+    reference: str = Field(alias="RmtInf")
+    other_name: str = Field(alias="RmtdNm")
+    other_iban: str = Field(alias="RmtdAcctIBAN")
+    category: Category | None = Field(alias="Category")
+    notes: str = Field(alias="Notes")
 
     @property
     def amount_signed(self) -> Decimal:
-        return self.amount * self.amount_type.sign
+        return self.amount * self.sign
+
+    @field_validator("sign", mode="before")
+    @classmethod
+    def get_sign(cls, input_value: str) -> int:
+        if input_value == "DBIT":
+            return -1
+        elif input_value == "CRDT":
+            return 1
+        else:
+            raise ValidationError(
+                f"Invalid amount type: {input_value}. Expected DBIT or CRDT"
+            )
 
     @field_validator("category", mode="before")
     @classmethod
@@ -55,7 +63,6 @@ class B4wExport(BaseModel):
         return category
 
 
-
 class Category(BaseModel):
     name: str = Field(pattern=r"[^:\r\n]+")
     parent: Category | None = None
@@ -79,4 +86,4 @@ class Category(BaseModel):
         return self.to_str()
 
     def __repr__(self):
-        return f"Category.from_str(\"{self.__str__()}\")"
+        return f'Category.from_str("{self.__str__()}")'