That's not an expired cert warning, those usually look like this:
View attachment 32604
note the error of "cert_date_invalid" and not "ssl_protocol_error"
It is version 18.0 (build 418)That error (from your desktop) is an expired cert error.
What version of 3CX (build number) and where is it running? Do you have ssh/backend access?

for some reason I didn't have PBXWizar folder, the PBxCofnfigTool.exe resides in BinBuild 418 is old, I think that is 18.0 update 2 or earlier?. I think that is the cause of your issue - you likely need 18.0 update 3 or newer
But... you can try to force the renewal
If that doesn't work, you might need to go in Settings / Parameters and Set or Add TEMPORARY_SELF_SIGNED_CERTIFICATE_GENERATED and give it value of 1.
- Go to Command Prompt.
- Type: “C:\Program Files\3CX Phone System\Bin\PBXWizard\PbxConfigTool.exe” -renew-certificates
- Press Enter and the result should look something like this:View attachment 32612
- Restart the nginx service
If that doesn't resolve it then you will need to check the log for the cause.
Sorry I can't be more help
the nginx server still in "stop pending" and the certificate error still there. I restarted all services at once. I don't know if this is correct or I shouldv'e restarted only the nginx server.The first error is just a path or spelling issue. Find the 3cx folder and the location of pbxconfigtool and run the command with the correct path.
I had to restart the hosting PC then all is good. the certificate now is renewed. but the problem is it is renewed for ONLY 3 months, any suggestions?the nginx server still in "stop pending" and the certificate error still there. I restarted all services at once. I don't know if this is correct or I shouldv'e restarted only the nginx server.
I'll wait and see for now. Please let me know if there is a special reastart for the services instead of restart all.
it is just busy time and the phones are beeing used constantly.
Founded in 2005, when VoIP was an emerging technology, 3CX has gone on to establish itself as a global leader in business communications.