As a test, If you try to reach directly the following links from any browser on your server:
http://www.solutionsam.com/solutions/pl/symantec_v2.pl.xml.zip
http://www.solutionsam.com/solutions/8_5_ru3/symantecinstallationmanagersetup.exe?symct=1585070825_990e5ed3fd787e26d0f56867af71560f'
It is most likely both will require to add credentials to the Proxy server:
If you add the proper credentials, it should download the files just fine.
The proper way to resolve this issue is:
1. Add the proper exclusion to your Proxy/Firewall rules
2. OR add the valid credentials for Proxy access under SIM:
a) SIM>Settings>Proxy Settings>Change>Add the requested information. Save changes and relaunch SIM.