Common causes of a failed integration / signature mismatch

The following will cause a signature mismatch or a payment to fail:

1. This is most likely caused if you generated the MD5 hashed string with the variables in the wrong order.
2. A required field is missing.
3. A field is greater than the allowable character length.
4. Any of the fields containing excess or invalid characters.
5. The parameter string has been URLencoded incorrectly. The resultant URLencoding must be in uppercase (eg. http%3A%2F%2F) and not lower case like http%3a%2f%2f, and spaces encoded as ‘+’.
6. The parameter string has not been trimmed of white spaces on the ends.
7. The passphrase, if used, must be identical on your PayFast account as well as the site, and may consist only of letters, numbers and -_/.
   Should you wish to set up recurring billing, then you will need to have a passphrase set and recurring billing enabled on your account in order to prevent the signature mismatch error.
8. You will need to ensure that the MD5 hash characters are in lower case.