[Python] PayFast signature (python): generated signature does not match submitted signature

I am trying to submit a PayFast payment using the API tools, in python rather than php (the docs recommended approach).

I am generating a signature like so:

import hashlib
import urllib.parse


def generate_signature(data: dict, passphrase: str) -> str:
"""
Generates an MD5 signature for PayFast API request.

- Assumes data is already in the correct order.
- URL encodes values with uppercase encoding.
- Uses '+' for spaces.
- Encodes passphrase before appending.
"""
encoded_params = []

for key, value in data.items():
if value: # Ignore empty values
encoded_value = urllib.parse.quote_plus(str(value)).upper() # URL encode & uppercase
encoded_params.append(f"{key.upper()}={encoded_value}")

# URL-encode the passphrase as well
encoded_passphrase = urllib.parse.quote_plus(passphrase).upper()

# Concatenate parameters
param_string = "&".join(encoded_params)

# Append encoded passphrase
param_string += f"&PASSPHRASE={encoded_passphrase}"

print(f"String before hashing: {param_string}")

# Generate MD5 hash
signature = hashlib.md5(param_string.encode("utf-8")).hexdigest()

print(f"Generated Signature: {signature}")
return signature



Following the docs for the signature generation, it looks like the parameter keys and values are meant to be upper case, and in order as specified by the optional form fields.

As far as I can tell, this is what I am doing, but I am still getting the error:

400 signature: Generated signature does not match submitted signature.


Here is what my generated signature looks like:

String before hashing:

MERCHANT_ID=11111111&MERCHANT_KEY=UAAAAAAAAAAHA&RETURN_URL=HTTPS%3A%2F%2AAAAAAAA.EXECUTE-API.AF-SOUTH-1.AMAZONAWS.COM%2FDEV%2FPAYFAST-REDIRECT&CANCEL_URL=HTTPS%3A%2F%2AAAAAAAAA6.EXECUTE-API.AF-SOUTH-1.AMAZONAWS.COM%2FDEV%2FPAYFAST-REDIRECT%3FSTATUS%3DFAILED&NOTIFY_URL=HTTPS%3A%2F%2AAAAAAAAA6.EXECUTE-API.AF-SOUTH-1.AMAZONAWS.COM%2FDEV%2FPAYMENTS%2FPAYFAST-NOTIFY&EMAIL_ADDRESS=JOHN.DOE%40GMAIL.COM&AMOUNT=300&ITEM_NAME=COOL&THING&ITEM_DESCRIPTION=BLAH&BLAH&BLAH&passphrase=PHRASEFROMSANDBOX


...which I've redacted of personal information.

I've tried different orders of the parameters, using lower case for the keys, lowercase for the keys and values. I cannot think of any other reasons why this format is incorrect.

Any help would be really appreciated!

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