Try each of the following steps until the issue is resolved.

Step #1: Make sure there is an Email Package set up for the Renewal template:
  1. Navigate to Memberships, then select the Membership Program
  2. Click Set up Membership Renewals
  3. Make sure an email package is selected for each type of renewal, as you see below:
User-added image

Step #2: Create a new membership renewal template that has Email as the user preference over mail:
  1. In Memberships, select the Membership Program
  2. Click Set up Membership Renewals
  3. At the bottom of the page, select Email instead of Mail for user preferences, as you see below
  4. Update the Name of the Membership Renewal to a unique name
  5. Click Save
User-added image