The Shelly1 can receive the relay closure then send an HTTP command to Blue Iris!
Read more about Shelly devices here ==>> Simple Blue Iris I/O using Shelly1 Wi-Fi Devices
Read more about HTTP commands in Blue Iris in BI's built-in "Help" at "Administration" => "HTTP Interface" for commands such as:
/admin?camera=x&profile=n[&lock=0/1] Temporarily force profile n on camera x (short name). Add &lock=1 to “hold” the the profile indefinitely. Use &profile=-1 to unlock and