After a fresh install of the OAuth Toolkit, the cluster property otk.port is found to be read-only. When attempting to edit the property you will receive the below error.
Release : 10.0
Component : API GATEWAY
If you are running OTK 4.3.1, this can be addressed by applying CR02 [https://support.broadcom.com/external/content/release-announcements/CA-API-Gateway-Solutions--Patches/3024].
In some cases, this can also be found in OTK 4.4. While a permanent fix is underway, an interim solution will be to define your own cluster property for the port and reference this in the #OTK Client Context Variables policy.