Schema validation for services tag

Hi
I used two services in my gitlab-ci but I faced this warning:

Schema validation: One of the following property sets is required: properties ‘when’ = delayed, ‘script’, ‘start_in’, property ‘script’, properties ‘when’ = delayed, ‘extends’, ‘start_in’, property ‘extends’, properties ‘when’ = delayed, ‘start_in’, ‘trigger’, or property ‘trigger’

and I don’t know which if the suggested options should I use…1

Please guide me
Thanks in advance