Olympz API deals with JSON requests. All the requests, excluding GET, should be signed by a secret key that will be also sent to Merchant. For signing you need to deliver the md5 hash from a request body with a secret a key concatenating. Then the delivered hash is used in the Sign header and sent together with the request. The example of the hash calculation in PHP:
Whereas Olympz sends the requests to the Merchant system using the same rules and keys. Your integration keys should be received via email from the manager.