Error: Can't mix management / non-management services.

When trying to add firewall access rule to allow web services HTTP and HTTPS firewall might give an error message Can't mix management/non-management services. This error may occur due to HTTP or HTTPS management service object selected in service group and that service group is used in firewall access rule. Here is the below screenshot showing the error message and Web Services group containing HTTP Management and HTTPS.

Remove management services HTTP Management from the service group and specify correct default service object HTTP or custom service objects.