from typing import Annotated
from pydantic.functional_validators import AfterValidator

# Customize the validation rule
def validate_payment_mthd(paymentMthd: str):
  possible_values = ['Credit card', 'Debit card', 'Digital wallet', 'Cash on delivery', 'Cryptocurrency']
  if paymentMthd not in possible_values:
    raise ValueError(f"Invalid paymentMthd, payment type must be one of {possible_values}")
  return storage

# Define the data model for a transaction record
class TxnModel(BaseModel):
  orderID: int = Field(strict=True)
  customerID: int
  productID: list[int]
  paymentMthd: Annotated[str, AfterValidator(validate_payment_mthd)]
  totalAmt: Annotated[float, Field(strict=True, gt=0)]
  invoiceTime: datetime

# Manually define a non-existent payment method
sample_txn['paymentMthd'] = 'Bitcoin'

try:
  # Validate the sample case against the schema
  TxnModel.model_validate(sample_txn)
  print("Validated successfully!")
except ValidationError as exc:
  # Print error messages for any validation error
  print("Validation Error:")
  print(exc.errors()[0]['ctx'])

# Output
# Validation Error:
# {'error': ValueError("Invalid paymentMthd, payment type must be one of ['Credit card', 'Debit card', 'Digital wallet', 'Cash on delivery', 'Cryptocurrency']")}