We use the Layer 7 Gateway Plugin in CMS -> Plugin Administration to configure/sync connection between API Portal and Gateway.
This option is missing in some environments.
API Developer Portal (2.x and 3.x)
Check the file permission for lrsgateway-conf.xml file under /opt/Deployments/lrs/server/webapps/ROOT/plugins
This file should have l7portal:portaluser as owners.
-rw-rw---- 1 l7portal portalusers 2438 date lrsgateway-conf.xml
Run this command to set the correct ownership
chown l7portal:portaluser /opt/Deployments/lrs/server/webapps/ROOT/plugins/lrsgateway-conf.xml
Restart apiportal service, for the changes to take effect.