How to enable Hash Validation on your account for use with Checkout
1. Log into your account.
2. On the menu, click administration> account settings> order settings.
3. Scroll down, and in the Payment Gateway section, under Security/Authentication, select the check box Require hash validation on all Payment Gateway transaction requests.
4. Enter a Hash Key. It must be at least 8 characters, it doesn't matter what those characters are.
5. Select (and make a note of) the type of Hash algorithm you are using (MD5 or SHA-1).
6. At the bottom of the page, click Update.
7. A confirmation box opens at the top of the browser window. Click OK.
Now that you have enabled Hash validation, click here for instructions on how to add Hash Validation to your Checkout Redirect Link.