To restrict a page, edit the relevant product and view the VISIBILITY options.
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Select a Group from the Security For Pricing Option to restrict who can see the price to a specific Member Group
Select a Group from the Security to Purchase option to restrict who can see buy the product to a specific Member Group
To give a user access to a password protected page, then you will need to create the member in the MEMBERS area,
Click the main MEMBER menu button, then choose Add Member from the options available.
If the user already exists, and you have restricted by Authorisation Level - then you need to select them and increase their security level to "Authorised User".
You can choose other access levels as appropriate. They must be higher than the security level set for the page. You can increase the password protection level for any page under page options tab, top right when editing page.
If you have restricted the page by Member Group, you will need to assign them to the relevant Member Group options. These can be found under the NEW GROUPS section on the right-hand side of the member record.