All the instructions I found on Google say there should be a button on this screen to report spam. But there never is one. Do I need to do something to enable it?
That's not an iMessage. That's an SMS text. Copy and paste the body WITHOUT clicking on the link and send that to 7726 (SPAM). That reports it to your carrier but doesn't seem to do much
Most cell companies provide their users with a email to text address. For example, a Verizon customer with cell number 123-456-7890 would receive SMS messages for emails sent to 1234567890@vtext.com.