This bug was discovered in Zabbix web service while working on ZBX-24850 in Zabbix agent 2.

Steps to reproduce:

1. Configure PDF scheduled reports as usual.
2. In Administration -> Geneal -> Other -> Frontend URL, configure a fronted URL containing IPv6 address. The correctness of the address may be checked by putting it to the browsers address bar. A public IP address or a link local address may be used. I observed no difference.
3. Test the scheduled report.

Result:
The report generation fails with the error message "Cannot fetch data.: Invalid cookie fields (-32602)." which is originated from Zabbix web service. See screenshot.

Expected:
Scheduled report is created and delivered by email. No errors are observed.
In ideal case, it should work with public and also link-local IP addresses