site does not respond to some sql injection commands [closed]

I work on a target that I know has SQL injection bug, because in this URL:*+form+aduan.emel 

I get this answer

Database Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘Select * form aduan.emel’ ORDER BY transaksi_aduan.no_pendaftaran asc’ at line 11

But some sql commands, like UNION SELECT @@version-- and Union+select+NUll,null-- don’t work!

When I submit them, the server responds with error 500.

Why does this happen? I think it is the firewall, is there any way to bypass it?

Notice: I have tried all the tamper options in sqlmap, but they didn’t work and the server returned: connection timed out to the target URL or proxy

I also tried –tor but it didn’t work.

Where is the problem?