The server worked fine until end of 2020 - we tried to download some packages and got 'Network error'.

So we tried something (in vale) and then we decided to run subscription-manager to resubscribe it.

Then from there we seemed ran into big mess, we searched lots posts and tried all they mentioned but no luck.
The issue is that we have an expired registration and whenever we tried to re-register (with subscription-manager command) it threw 'Network error', in /var/log/rhsm/rhsm.log, we see 'Tunnel connection failed: 407 Proxy Authentication Required'.

So we know something wrong with the proxy. We now run two commands in row: 1) subscription-manager config --server.proxy_hostname=aaa --server.proxy_port=80 --server.proxy_user=bbb --server.proxy_password=ccc; 2) subscription-manager register --username=xxx --password=yyy --force, but it still threw 'Network error' in command output and the 407 error in the log file.


Finally we turned to 'subscription-manager-gui', and configured (by adding proxy server/username/password) and tested proxy connection success (and click 'Save', which saved all the above info in /etc/rhsm/rhsm.conf), from the GUI, we can see that the subscription is expired, but when we tried to remove it, we got our old friend 'Network error'. When we tried to 'Update' in 'All Available Subscriptions', it error out with 'Unable to search for subscriptions: Error updating system data on the server, see /var/log/rhsm/rhsm.log for more details'. Then in /var/log/rhsm/rhsm.log, we see the following (same errors) -
.......
...Response: 400
...JSON parsing error: No JASON object could be decoded
...Network error code: 400
...Unable to reach server using cached status
.......

We also included the redhat subscription account info in /etc/rhsm/rhsm.conf in [server] section as follow -
username=ppp
password=qqq

Can anybody point out why the GUI connection tested success but it still gave 'Network error' and '400' in log file? What we did wrong and what we should do to fix it?

TIA

No idea, since there's next to nothing in the way of details. You say you:

• "Downloaded some packages" - but don't say which ones, where you downloaded them from, or why you downloaded them versus having yum install them.
• "tried something (in vale) - but don't say what.
• "searched lots of posts and tried all" - again, no idea WHAT you tried.

...and you don't tell us what version of Red Hat Enterprise you're using, or if you're able to connect to ANYTHING on the Internet from that system.

If you're having a subscription problem with RHEL, the best people to contact would be Red Hat support, since you're paying for it. And if you're using a developer version, there's not much we can help with when we have no idea what you've done/tried so far.