Generally speaking, to configure Mercury Hosted Checkout you will need to:
A) Get the Hosted Checkout password from your Mercury Portal and
B) Configure the Payment Method on your website.
NOTE: To configure your reCommerce website for Mercury Hosted Checkout you will need to have a Hosted Checkout account with Mercury.
A) To get the Hosted Checkout password from your Mercury Portal:
1) Login to your Mercury Portal https://portal.mercurypay.com
2) Select Account Settings
3) Under HostedCheckout Password Management, select the terminal for which you to obtain a password and click Continue.

NOTE: If you have a Hosted Checkout Account with Mercury and don't see the HostedCheckout Password Management area, you need to call Mercury Technical Support Department to fix.
4) Select Generate Password

5) Copy the password. We will paste it in to your website admin section.
6) Click Save
B) To configure your website's Payment Method you must first Login to the Admin section of your website.
1) Click the Settings menu
2) Click the Payment Options menu item

Enable the Mercury payment method

Click Configure

1) Add your MerchantID to the MPS MerchantID field.
2) Paste the password, that you got from the Mercury Portal, into the MPS password field
3) Change the test mode to Live.

4) Click Update
5) Click Apply Changes

How do you know all is well? Test it!! Actually, go through the entire checkout process.
I hope this helps.
A) Get the Hosted Checkout password from your Mercury Portal and
B) Configure the Payment Method on your website.
NOTE: To configure your reCommerce website for Mercury Hosted Checkout you will need to have a Hosted Checkout account with Mercury.
A) To get the Hosted Checkout password from your Mercury Portal:
1) Login to your Mercury Portal https://portal.mercurypay.com
2) Select Account Settings
3) Under HostedCheckout Password Management, select the terminal for which you to obtain a password and click Continue.

NOTE: If you have a Hosted Checkout Account with Mercury and don't see the HostedCheckout Password Management area, you need to call Mercury Technical Support Department to fix.
4) Select Generate Password

5) Copy the password. We will paste it in to your website admin section.
6) Click Save
B) To configure your website's Payment Method you must first Login to the Admin section of your website.
1) Click the Settings menu
2) Click the Payment Options menu item

Enable the Mercury payment method

Click Configure

1) Add your MerchantID to the MPS MerchantID field.
2) Paste the password, that you got from the Mercury Portal, into the MPS password field
3) Change the test mode to Live.

4) Click Update
5) Click Apply Changes

How do you know all is well? Test it!! Actually, go through the entire checkout process.
I hope this helps.