V3 - Overview

Fat Zebra provides a hosted payment page for merchants who wish to remove all PCI-DSS scope from their systems. This is known commercially as PayNow. Please note that merchants and service providers are required to complete Self-Assessment Questionnaire A to adhere to PCI DSS Compliance.

Currently the hosted payment page supports three methods of implementation:

  • Standard Hosted Page (i.e. redirection from the merchants website to the payment page)
  • IFrame embedded page
  • Accounting platform payment page (for example Xero or Saasu)

The V3 UI looks like this, but it can be re-styled using the css parameter, documented below:


The data sent between the merchant and Fat Zebra, and from Fat Zebra to the merchant is sent in the request URL - to ensure that this has not been tampered with the payload includes a verification value, which is a signed-hash based on the payload values, using a shared secret between the merchant and Fat Zebra. This process has been closely modeled on the Fat Zebra Direct Post method - it is recommend you review this documentation for further details which may not be covered here.


There are two different URLs for the PayNow service - one for the Sandbox environment and one for the Live environment:

EnvironmentBASE URL


In order to direct the customer to the hosted payment page the merchants website should prepare the following URL and either use this as the redirect destination, or as the IFRAME source:


URL Parameters

The following parameters are required and are used to build the URL which the user should be redirected to (or as the source for the IFRAME):

amountnumberThe amount of the transaction, as a decimal value.

For currencies which do not make use of the decimal/cent value this should be omitted as 00 (e.g. 300.00 for ¥300)
hashstringThe hash is a MD5 hexdigest of a string compiled from the request parameters.
See below (Verification Value Calculation) for more details.
referencestringThe invoice number or order reference
currencystring (3 characters)The ISO-4217 3-letter currency code for the transaction
usernamestringThe merchants Fat Zebra username


Provide any of the following as query parameters to specify display options - these are optional parameters:

iframebooleanIndicates whether to show the stripped-down iframe layout or notfalse
show_emailbooleanIndicates whether to show and require the email field or nottrue
show_extrasbooleanIndicates whether to display the invoice number and the amount to the customertrue
return_pathstringThe return URL for the transaction success - if this is omitted the result will be displayed on screen to the customer
Note: if the a URL is specified it must be included in the verification hash. This may be a non-resolving URL for callback handling in mobile
applications if required (e.g. paymentcallback://....)
tokenize_onlybooleanIf this is set the card will not be charged, and will only be tokenized for future usefalse
authbooleanIf this is set the card being tokenized or the transaction processed will have an auth for the amount specified in the request performed. This can be used to verify the card
details are valid before storing.
button_textstringSpecifies the text to be displayed for the submit button (e.g. Pay Now or Submit)Pay Now
hide_logosbooleanShows or hides the card logosfalse
return_targetstringWhen used in iframe mode (iframe=true) specifies where the target for the form post (e.g. post back to _parent, _self or speficied)empty
postmessagebooleanWhen used in iframe mode (iframe=true) specifies that the response should be sent using postMessage instead of redirectingfalse
cssstringHTTPS URL for external CSS - this must be a valid HTTPS URL, and serve up a valid CSS file. Depends on css_signatureempty
css_signaturestringHMAC-MD5 of the css URL with the shared secret to sign the request.

For example, the CSS signature for https://example.com/example.css with a shared secret of "TEST" would be:


Importantly: this hash is not a hash of the contents of the CSS file -- only the URL of the CSS file.
logo_urlstringHTTPS URL for the merchant logo. This must be a valid HTTPS URL and serve up a valid image file.empty
hide_buttonbooleanHides the button from the checkout form for when the checkout should be triggered by postMessage. Note this option is dependent on the v2 layout.false
cardsstring, comma separatedSpecifies the whitelist or blacklist of accepted cards. If the string is prefixed with an exclamation mark (!) the cards listed will not be permitted.
Possible values are: AMEX, JCB, VISA, MasterCard, Diners


!AMEX,JCB - disabled AMEX and JCB

VISA,AMEX - enabled only VISA and AMEX

Note if this field is present it is included in the end of the verification value string.
surchargebooleanSpecifies if a surcharge will be applied. Surcharge rates are set in the Surcharging section of the Merchant Dashboard.

Note: if the surcharge field is set to true, “:true” must be appended in the verification hash.
hide_card_holderbooleanSpecifies if the card holder name field should be hiddenfalse

Note on external CSS: When external CSS specified in the options the hosted payment page a number of verification and sanitisation steps are taken before rendering the CSS in the page, including:

  • Verifying the URL specified is served over HTTPS and is in-fact a CSS file
  • Verifying that the css_signature matches the URL
  • Scrubbing any potentially dangerous CSS statements from the file

After successful verification and sanitising , the filtered CSS is cached by the Hosted Payment Page for 5 minutes. If the cache needs to be updated, the following options are available:

  • Change the URL and update the signature to reflect - the CSS cache uses the filename and merchant ID as the cache key, so changing this will force the cache to be updated

Verification Value Calculation

There are two points of verification for requests - once when the request is received by Fat Zebra (when the hosted page is rendered to the user), and once when the response is returned to the merchant - it is important that the response is verified by the merchant to ensure that the response has not been tampered with by malicious users.

Request Verification (Redirect to Fat Zebra)

The request received by Fat Zebra will be verified with the following steps:

  1. The reference, currency, amount, and if present, hide_card_holder will be concatenated into a string, joined by colons:
https://paynow.pmnts.io/v3/samsbooks/INV1121/AUD/100.25/xxxxxxxxxxx&hide_card_holder=true -> "INV1121:100.25:AUD:true"

If hide_card_holder is not included, it will be omitted:

https://paynow.pmnts.io/v3/samsbooks/INV1121/AUD/100.25/xxxxxxxxxxx&hide_card_holder=true -> "INV1121:100.25:AUD"
  1. The value of this string will then be hashed with a HMAC-MD5, using the shared-secret known by Fat Zebra and the merchant (please contact Fat Zebra Support if you are unsure of where to find this shared secret).
shared_secret = "<<sharedSecret>>"
verification = hmac_md5(shared_secret, "INV1121:100.25:AUD:true")

Response Verification (Purchases)

For purchases the response verification will consist of the response code, success indicator, amount, currency, transaction ID and the card token:

https://www.samsbooks.com/payment/callback?r=1&successful=true&amount=10025&currency=AUD&id=001-P-ABCDG1124&token=abcd1234&v=xxxxx....... -> "1:true:10025:AUD:001-P-ABCDG1123:abcd1234"
shared_secret = "<<sharedSecret>>"
verification = hmac_md5(shared_secret, "1:true:10025:AUD:001-P-ABCDG1123:abcd1234")
# v == verification should be true

The response for purchases will also include the following:

messagestringAny messages relating to the transaction
amountintegerThe amount, as an integer
referencestringThe transaction reference
idstringThe Fat Zebra transaction ID
currencystringThe ISO-4217 3-letter currency code for the transaction
card_numberstringThe masked credit card number (e.g. 512345XXXXXXXX2346)
card_holderstringThe card holders name
card_expirydate (mm/yyyy)The card expiry date
card_typestringThe card type of the credit card used. Possible values are:
VISA, MasterCard, AMEX, JCB, Diners, Discover, China UnionPay, Unknown
successfulbooleanIndicator of transaction success

Response Verification (Tokenization)

For tokenization the response verification will consist of the response code, and the card token:

https://www.samsbooks.com/payment/callback?r=1&token=abcd1234&v=xxxxxxxxx........ -> "1:abcd1234"
shared_secret = "<<sharedSecret>>"
verification = hmac_md5(shared_secret, "1:abcd1234")
# v == verification should be true

The response for tokenization will also include the following:

card_numberstringThe masked credit card number (e.g. 512345XXXXXXXX2346)
card_holderstringThe card holders name
card_expirydate (mm/yyyy)The card expiry date
tokenstringThe token representing the card in Fat Zebra systems

Response Codes

The following response codes are used when a redirect URL is provided:

2Declined - examine the message parameter for possible explanations
94Cancelled - the merchant clicked the Cancel button on the payment or checkout form
95Merchant Not Found - possible incorrect username
96Reference not unique
97Validation error - check the errors[] parameters for error messages
99Invalid Verification - the verification value does not match the parameters supplied
999Gateway error - an unknown error has occurred and the merchant should investigate with Fat Zebra Suppor


Standard Fat Zebra test procedures apply for the Hosted Payment Page. You can use our test card numbers to check the behaviour of the hosted payment page.