Steps to reproduce:

1. Go to Administration > General > Autoregistration

1. Disable No encryption

1. Enable PSK

1. Press 'Change PSK'

1. Enter a PSK identity

1. As "PSK", enter a 32 character long HEX string, where at least one alphabetical character are uppercase (ABCDEF instead of abcdef).

1. Configure agent2 with PSK autoregistration (on several machines) as described in documentation, with the PSK identity and PSK that the server was configured to accept.

Result:
Some few hosts are autoregistrered just fine.
Then zabbix-server.log is filled with following 2 error messages (anonymized).

• autoregistration from "10.11.12.13" denied (host:"myHost13" ip:"10.11.12.13" port:10050): connection used PSK which is not configured for autoregistration
• host PSK and autoregistration PSK have the same identity "SECRET_ID_123_ABC" but different PSK values, autoregistration will not be allowed

No more hosts are autoregistrered after this.

To get autoregistration to start again:

1. Delete all hosts in zabbix frontend.
2. Restart zabbix-server service in terminal
3. Expect autoregistration to stop working after a few hosts have autoregistrered.

Self-Help Fix:

Configure the server with a PSK that uses only lowercase letters.

The agent’s TLSPSKFile appears to be case-insensitive, meaning it can contain either uppercase or lowercase characters without issue.

Proposed Fix:
Developer could normalize the PSK key by converting it to lowercase after the API call to ensure consistency and prevent unexpected failures.