Deep link for email template format

Summary:

Hi all,

I am working on an email template that is supposed to link to a specific opportunity subtab. I am getting to the Opportunity List but cannot get the syntax right for opening the opportunity. It is putting the opportunity ID in the URL but I may not have it positioned correctly. Can someone please show me where I am going wrong on this?

Content (required):

Note: This is an email template for a custom object that is associated with an opportunity. The requirement is to link verbiage in the email back to the opportunity rather than the custom object. In the custom object we are using a custom field called OPTYNum_c to hold the ID field. Environment name in the link below is a substitute for the actual CRM instance. That part works as espected.