Daily email alert for missing related object in opportunity

Hi there,

I want to create a workflow that will send an email alert to opportunity owners if a specific related object has not been created.

I've created a schedule-triggered flow (8am daily), related object Opportunity, and condition is that Number of related object is null and value is true.

Then I've set up an email alert that goes out to the Opportunity Owner, and Set Input Values for the Selected Action is Record ID.

I enabled all emails in my sandbox for testing, but I'm not receiving anything, so assuming the flow is wrong.

Any advice?

Thank you!