In Marketing Cloud, I am facing error message : "A profile center link is missing from this email. For template based email, please contact our customer service."
What should I do ?
You need to add the required Personalization Strings to your email HTML as outlined in the error message:
There's one circumstance under which Adam's answer is not correct - if you are using your own CRM/website for unsubscribes. If so, talk to your AE or support to have that warning disabled on your account.
Just to add to this, we found we were getting click throughs using the scripting hack from Adam so changed to the solution from Data_Kid.
This sometimes displayed the ridiculously long link for (at least) Windows users on Outlook 16 so am now using:-
<div style="display:none"><a href="%%profile_center_url%%">.</a></div>
which displays a fullstop at worst.