Definition: POST /v1/merchantsites
For each of your websites you can create a different Merchant Site, which will have its own API Key.
Please note that the requests for the Merchant Sites will use the API Key created at merchant account level.
Request:
POST https://paytest.smart2pay.com/v1/merchantsites
Authorization: Basic MzAyMDE6aEo1Um9iWXg5cjdGZk53Q3ZIWTlMWEhxcXIrRkV6cmM3YUp2UVFrNEdhejFtZzdSeXk=
{
  "MerchantSite": {
    "URL": "http://www.test.com",
    "Active": true,
    "NotificationURL": "http://www.test.com/notifications.node",
    "IPList": "82.208.151.136",
    "Alias": "Test website_1",
    "Details": {
      "Name": "Stichting Smart2Pay",
      "Country": "PL",
      "City": "Warsaw",
      "Email": "test@test.com", 
      "Address": "BRINK 27C",
      "BankName": "ING",
      "AccountIBAN": "PL641050008610000023537933350",
      "AccountSWIFT": "1000002353794650",
      "BankSWIFTID": "ABNDDEFFXXX",
      "BankCode": "BTRLRO22",
      "VATNumber": "34206701",
      "RegistrationNumber": "NL 813236460B01",
      "MCC": "5945",
      "MainBusiness": "Hobby, Toy, and Game Shops"
    }
  }
}
{"MerchantSite":{"hint":"MerchantSite structure","regexp":"","type":"object","ID":{"hint":"GlobalPay website ID, a unique number that identifies the website in the GlobalPay system.","regexp":"^\\d{1,12}$","type":"int"},"MerchantID":{"hint":"ID of merchant that owns the site","regexp":"^\\d{1,12}$","type":"int"},"Created":{"hint":"Date and time when the site was created.","regexp":"","type":"datetime"},"URL":{"hint":"The URL of the website","regexp":"^(http?s?:\\\/\\\/)?(www)?(([0-9a-zA-Z]+)([\\-_])*)+(\\.([\\-_0-9a-zA-Z]+)(\\\/)*)+(([\\\/?#\\?&=\\-_0-9a-zA-Z])\\.?)*$","type":"string"},"Active":{"hint":"A flag showing if the website is active or not, defaults to false if not sent.","regexp":"","type":"bool"},"NotificationURL":{"hint":"An URL where GlobalPay sends notifications when a transaction changes its status. HTTPS must be used!","regexp":"^(http?s?:\\\/\\\/)?(www)?(([0-9a-zA-Z]+)([\\-_])*)+(\\.([\\-_0-9a-zA-Z]+)(\\\/)*)+(([\\\/?#\\?&=\\-_0-9a-zA-Z])\\.?)*$","type":"string"},"Alias":{"hint":"Site alias, an alternative name that identifies the website in the GlobalPay system.","regexp":"^.{1,255}$","type":"string"},"ApiKey":{"hint":"The API key used to authenticate the requests to the REST API.","regexp":"^.+$","type":"string"},"IPList":{"hint":"A list of IPs that will be allowed to perform requests towards GlobalPay.\r\nAccepts single IPs, ranges and\/or CIDR notation.","regexp":"^(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3},?)?|^(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\\/\\d{1,2},?)?|^((\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3})-(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}),?)?$","type":"string"},"Details":{"hint":"In some cases we send various details about the payment (e.g. Reference Number and Bank Details of the Customer for Bank Transfer payments).","regexp":"","type":"object","Reasons":{"hint":"The reasons why the payment got to this status.","regexp":"","type":"array of objects","Code":{"hint":"The id of the message type transmitted in the response. See our section GlobalPay Return Codes for a complete description.","regexp":"","type":"int"},"Info":{"hint":"The message body","regexp":"","type":"string"}},"Name":{"hint":"The name of the site","regexp":"^.{1,50}$","type":"string"},"Country":{"hint":"The country of the website. Format is according to ISO-3166-1 alpha-2, a two-letter code.","regexp":"^[a-zA-Z]{2}$","type":"string"},"City":{"hint":"City name","regexp":"^.{1,50}$","type":"string"},"Email":{"hint":"Site contact email address","regexp":"^[a-zA-Z0-9\\._%+-]{1,100}@[a-zA-Z0-9\\.-]{1,40}\\.[a-zA-Z]{1,8}$","type":"string"},"Address":{"hint":"Site contact address","regexp":"^.{1,512}$","type":"string"},"BankName":{"hint":"The name of the Bank","regexp":"^.{1,50}$","type":"string"},"AccountIBAN":{"hint":"Site account IBAN","regexp":"^[a-zA-Z]{2}[0-9]{2}[a-zA-Z0-9]{4}[0-9]{7}([a-zA-Z0-9]?){0,16}$","type":"string"},"AccountSWIFT":{"hint":"Site account SWIFT","regexp":"^\\w{1,30}$","type":"string"},"BankSWIFTID":{"hint":"Swift ID, a unique identification code for a particular bank.","regexp":"^[a-zA-Z]{6}[a-zA-Z0-9]{2}([a-zA-Z0-9]{3})?$","type":"string"},"BankCode":{"hint":"Site\u2019s bank code. Also known as BIC or Swift_BIC. Bank Identifier Code (BIC), a unique identification code for a particular bank (consists of 8-11 alphanumeric characters).","regexp":"^[a-zA-Z]{4}[a-zA-Z]{2}[a-zA-Z0-9]{2}[XXX0-9]{0,3}","type":"string"},"VATNumber":{"hint":"Site VAT number","regexp":"^.{1,50}$","type":"string"},"RegistrationNumber":{"hint":"Site registration number","regexp":"^.{1,50}$","type":"string"},"MCC":{"hint":"Merchant Category Code (MCC), a four-digit number listed in ISO 18245 for retail financial services, used to classify the business by the type of goods or services it provides.","regexp":"^[0-9]{1,10}$","type":"string"},"MainBusiness":{"hint":"Site company main business","regexp":"^.{1,100}$","type":"string"}}}} 
Response:
HTTP/1.1 201 Created
Content-Type: application/json; charset=utf-8
{
    "MerchantSite": {
      "MerchantID": 1045,
      "ID": 43078,
      "Created": "20180104161226",
      "URL": "http://www.test.com",
      "Active": true,
      "NotificationURL": "http://www.test.com/notifications.node",
      "ApiKey": "aaqosSwikwduK2l72PAGMa8kaLqHuB3hH39/ECcqaD5hW69aSX",
      "Alias": "Test website_1",
      "IPList": "82.208.151.136",
      "Details": {
        "Reasons": null,
        "Name": "Stichting Smart2Pay",
        "Country": "PL",
        "City": "Warsaw",
        "Email": "test@test.com",
        "Address": "BRINK 27C",
        "BankName": "ING",
        "AccountIBAN": "PL641050008610000023537933350",
        "AccountSWIFT": "1000002353794650",
        "BankSWIFTID": "ABNDDEFFXXX",
        "BankCode": "BTRLRO22",
        "VATNumber": "34206701",
        "RegistrationNumber": "NL 813236460B01",
        "MCC": "5945",
        "MainBusiness": "Hobby, Toy, and Game Shops"
        }
    }
}
{"MerchantSite":{"hint":"MerchantSite structure","regexp":"","type":"object","ID":{"hint":"GlobalPay website ID, a unique number that identifies the website in the GlobalPay system.","regexp":"^\\d{1,12}$","type":"int"},"MerchantID":{"hint":"ID of merchant that owns the site","regexp":"^\\d{1,12}$","type":"int"},"Created":{"hint":"Date and time when the site was created.","regexp":"","type":"datetime"},"URL":{"hint":"The URL of the website","regexp":"^(http?s?:\\\/\\\/)?(www)?(([0-9a-zA-Z]+)([\\-_])*)+(\\.([\\-_0-9a-zA-Z]+)(\\\/)*)+(([\\\/?#\\?&=\\-_0-9a-zA-Z])\\.?)*$","type":"string"},"Active":{"hint":"A flag showing if the website is active or not, defaults to false if not sent.","regexp":"","type":"bool"},"NotificationURL":{"hint":"An URL where GlobalPay sends notifications when a transaction changes its status. HTTPS must be used!","regexp":"^(http?s?:\\\/\\\/)?(www)?(([0-9a-zA-Z]+)([\\-_])*)+(\\.([\\-_0-9a-zA-Z]+)(\\\/)*)+(([\\\/?#\\?&=\\-_0-9a-zA-Z])\\.?)*$","type":"string"},"Alias":{"hint":"Site alias, an alternative name that identifies the website in the GlobalPay system.","regexp":"^.{1,255}$","type":"string"},"ApiKey":{"hint":"The API key used to authenticate the requests to the REST API.","regexp":"^.+$","type":"string"},"IPList":{"hint":"A list of IPs that will be allowed to perform requests towards GlobalPay.\r\nAccepts single IPs, ranges and\/or CIDR notation.","regexp":"^(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3},?)?|^(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\\/\\d{1,2},?)?|^((\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3})-(\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}),?)?$","type":"string"},"Details":{"hint":"In some cases we send various details about the payment (e.g. Reference Number and Bank Details of the Customer for Bank Transfer payments).","regexp":"","type":"object","Reasons":{"hint":"The reasons why the payment got to this status.","regexp":"","type":"array of objects","Code":{"hint":"The id of the message type transmitted in the response. See our section GlobalPay Return Codes for a complete description.","regexp":"","type":"int"},"Info":{"hint":"The message body","regexp":"","type":"string"}},"Name":{"hint":"The name of the site","regexp":"^.{1,50}$","type":"string"},"Country":{"hint":"The country of the website. Format is according to ISO-3166-1 alpha-2, a two-letter code.","regexp":"^[a-zA-Z]{2}$","type":"string"},"City":{"hint":"City name","regexp":"^.{1,50}$","type":"string"},"Email":{"hint":"Site contact email address","regexp":"^[a-zA-Z0-9\\._%+-]{1,100}@[a-zA-Z0-9\\.-]{1,40}\\.[a-zA-Z]{1,8}$","type":"string"},"Address":{"hint":"Site contact address","regexp":"^.{1,512}$","type":"string"},"BankName":{"hint":"The name of the Bank","regexp":"^.{1,50}$","type":"string"},"AccountIBAN":{"hint":"Site account IBAN","regexp":"^[a-zA-Z]{2}[0-9]{2}[a-zA-Z0-9]{4}[0-9]{7}([a-zA-Z0-9]?){0,16}$","type":"string"},"AccountSWIFT":{"hint":"Site account SWIFT","regexp":"^\\w{1,30}$","type":"string"},"BankSWIFTID":{"hint":"Swift ID, a unique identification code for a particular bank.","regexp":"^[a-zA-Z]{6}[a-zA-Z0-9]{2}([a-zA-Z0-9]{3})?$","type":"string"},"BankCode":{"hint":"Site\u2019s bank code. Also known as BIC or Swift_BIC. Bank Identifier Code (BIC), a unique identification code for a particular bank (consists of 8-11 alphanumeric characters).","regexp":"^[a-zA-Z]{4}[a-zA-Z]{2}[a-zA-Z0-9]{2}[XXX0-9]{0,3}","type":"string"},"VATNumber":{"hint":"Site VAT number","regexp":"^.{1,50}$","type":"string"},"RegistrationNumber":{"hint":"Site registration number","regexp":"^.{1,50}$","type":"string"},"MCC":{"hint":"Merchant Category Code (MCC), a four-digit number listed in ISO 18245 for retail financial services, used to classify the business by the type of goods or services it provides.","regexp":"^[0-9]{1,10}$","type":"string"},"MainBusiness":{"hint":"Site company main business","regexp":"^.{1,100}$","type":"string"}}}}