You can determine the upload URL by issuing the following command:

$AOM_HOME/scripts/emsctl status

Example:

$AOM_HOME/scripts/emsctl statusOracle Enterprise Manager Cloud Control 13c Release 5
Copyright (c) 2017, 2021, Oracle Corporation. All rights reserved.
------------------------------------------------------------------
Always-On Monitoring Version : 13.5.0.0.0
Always-On Monitoring Home : /mycomputer/ems
Started At : December 23, 2019 2:24:25 PM PST
Last Repository Sync : December 23, 2019 2:25:49 PM PST
Upload URL : https://myserver:8081/upload
Always-On Monitoring Process ID : 24924
Always-On Monitoring Repository : myserver.myco.com:15044:sarview
Enterprise Manager Repository : myserver.myco.com:15044:sarview
Notifications Enabled : true
Notification filters - Alert types
    Target Availability (targetAvail) : true
    Metric Alerts (metricAlert) : true
    Metric Errors (metricError) : false
Notification filters - Severity
    Fatal (fatal) : true
    Critical (critical) : true
    Warning (warning) : true
    Advisory (advisory) : false
    Informational (informational) : false
    Clear (clear) : false
Total Downtime Contacts Configured : 1

You can verify the setting in the OMS by using the emctl get property command.

You can verify the setting on a particular Agent by looking at $AGENT_HOME/sysman/config/emd.properties and searching for EMS_URL.