Would like to enable messages and reminders but get an error

I have tried to send messages and reminders but with all users except administraters I’m getting the following message “Apache/2.4.48 (Win64) OpenSSL/1.1.1k PHP/7.4.20 Server at 192.168.1.100 Port 80”. Do I need to activate something? I 'm able to message other admins.

Thanks for the help in advance.