Trying to get New Member, Member Renewal Contribution working
My guess is that you're sending emails out using CiviMail or the &quot;send mail to contacts&quot; search action.  This won't pick up the membership ID, because a contact can have multiple memberships and there's no way to know which to use.
I believe at present the only way (in CiviCRM core) to use the membership ID token is when using Scheduled Reminders (**Administer menu &gt;&gt; Communications &gt;&gt; Scheduled Reminders).  There's ongoing work to use the new token processor in other areas of CiviCRM, which would allow using this token elsewhere.
If you only have one active membership per contact, you can install Fuzion Tokens, which has a &quot;latest membership ID&quot; token.  This works for contacts because it eliminates the ambiguity of which membership is meant.