This Knowledge Base Article explains why prices or Tax and Service Fees may vary between Travelnow, and the results returned via API.
The rates returned via API are determined by the TPID selected for the request.
The TPID is integer number, generated based on the provided customerIpAddress, currencyCode and locale.
Travelnow.com uses a default TPID based on the en_GB locale, with a dynamic IP Address based on the location from the request is made, and a currency that can be changed by the user at any time.
On the other hand, the API uses en_US as a default locale, and in accordance with specific country policies on Tax Rates, prices may or may not vary due to the use a different locale.
In order to make sure you get the same results via API as the ones provided by Travelnow, please make sure you are using the exact same customerIpAddress, currencyCode and locale.
In most cases, changing the locale in the API to en_GB will provide price and tax parity. If this does not solve the issue, please also set the customerIpAddress parameter to your IP Address, and double check to make sure you are using the same currency on both Travelnow and the API.