I see two most possible reasons:
1. Server misconfiguration;
2. Code integrity violation.
What's in the error log of the web server?
Probably it attempts to get a
file named
update instead of transferring the processing of incoming request to Mibew Messenger. It could be either because of some specific rules established for your vhost in the configuration of Apache (or frontend proxy if there are any), or because of broken routing table inside of Mibew Messenger.
The former is located in
configs/routing.yml file and should contain the route to
update path. The sha256 check sum for the routing table for Mibew Messenger 3.2.2 is
37b59c7cb5f4b6838eb9a2ba6c0fee12539e2429c2ce9ad41676fffa5344884d.