<ol>
<li>Sign in to your <a href="https://account.authorize.net/">authorize.net</a> account.</li>
<li>Go to "Account"; in the "Security Settings" section, select "API Credentials & Keys" link.</li>
<li>Copy the  API Login ID value.</li>
<li>Go to X-Cart and paste the API Login ID value you have copied into the "API Login ID" field on the payment method settings page.</li>
<li>If you haven't yet created a Transaction key, do so. Copy the value of your Transaction key and paste it into the "Transaction key" field on the payment method settings page in X-Cart.</li>
<li>Again, go to "Account"; in the "Security Settings" section, select "Manage Public Client Key".</li>
<li>If the Client key has not yet been created, choose to create a Client key. Copy the Client key value and paste it into the "Public key" field on the payment method settings page in X-Cart.</li>
</ol>