To allow workflow to use add-in permissions

  • On the site that you are making the work flow click the settings icon in the upper right corner of the screen and go to Site Settings
  • In the Site Actions section, select Manage site features
  • Locate the feature called Workflows can use app permissions and click Activate

References:

https://docs.microsoft.com/en-us/sharepoint/dev/general-development/create-a-workflow-with-elevated-permissions-by-using-the-sharepoint-workflo

https://stackoverflow.com/questions/27845480/why-is-app-step-greyed-out-in-sharepoint-designer