Before you perform test transactions, it's important to check the connectivity to the MasterCard Payment Gateway.
To do this, try and access the following URL through a web browser:
REST:https://eu-gateway.mastercard.com/api/rest/version/1/information
NVP:https://eu-gateway.mastercard.com/api/nvp/version/1/information
If the gateway is able to process requests, i.e., if successful, the "information" file displays {"status":"OPERATING"} in the JSON format for the REST protocol. NVP displays status=OPERATING.