Y aren't doing anything wrong. When you copy text directly from Word, it sometimes brings along a lot of hidden formatting code behind the scenes. When you paste that into the Constant Contact editor, that hidden code often breaks the link.
The Fix:
Paste as Plain Text : Instead of a normal paste, try using Ctrl + Shift + V on PC or Cmd + Shift + V on Mac. This strips away all that hidden Word formatting and just pastes the clean link.
Use the Link Tool: Instead of pasting the link directly into the text body:
Copy the web address you need.
In Constant Contact, highlight the text you want to be clickable.
Click the Link icon in the toolbar.
Paste your URL there.