There are a couple of settings on the Hosted Page configuration on the Moneris account that should be enabled when using the Moneris payment method on a Pressero site.
The Transaction Type will be Purchase, Payment Methods will be Credit Cards, and for the Response Method settings it should be set for the "Sent to your server as a POST" option.
To get the values for Approved URL and Declined URL, look at the Settings > Payments page of your site in Pressero. Expand the settings for the payment method enabled on that site and find the Post Back URL value just below the Enable Range setting. That value will be used for both the Approved URL and Declined URL values on the Hosted Page configuration.
If you continue to have difficulty setting up your Moneris payment method, please submit a ticket to us at support.aleyant.com