This post shows how to fix this error that occurs during execution of workflow for a list:
HTTP Unauthorized to https://<sharepoint_url>/_api/sp.utilities.utility.SendEmail Correlation Id: <some_id> Instance Id: <some_id>
Access denied. You do not have permission to perform this action or access this resource.
Possible Fix 1: Permission error for user
Check if the user at least has the permission to contribute to the involved list. They should be assigned to one of the group that has such permission. You can check it under Site settings > People and groups under Users and Permissions.
Possible Fix 2: Feature not activated
Make sure the feature “Limited-access user permission lockdown mode” is not activated. You can check it under Site settings > Site collection features under Site Collection Administration
Possible Fix 3: Feature activated
Make sure the feature “Workflows can use app permissions” is activated. You can check it under Site settings > Manage site features under Site Actions
Possible Fix 4: SharePoint group visibility
This fix is particular when the workflow gets suspended without sending mail to members of a SharePoint group. When a To or a CC field has SharePoint group as a recipient,
- Workflow initiator should either be a member of that particular group
- Visibility of that group should be available to everyone
You can check the group settings under Site settings > People and groups under Users and Permissions > select the SharePoint group that is a recipient > Settings (drop-down) > Group Settings (drop-down option)
If you are not ready to change the Group Settings to Everyone. Then, you need to replace the recipient in To or CC field from SharePoint group to a individual persons.