When trying to add the K2 for SharePoint app to your app catalog, you may receive the following error:
Sorry, something went wrong with adding the app. Click to retry.
This occurs when Azure Access Control Services (ACS) is enabled in SharePoint.
This is an issue that occurs with any provider-hosted, high trust app due to an issue in SharePoint. To resolve this issue, follow the steps in the Microsoft article High Trust provider Apps (On-Premise environment) won’t publish when Azure App Proxy enabled in web application service application proxy Association
You can find additional information about this issue at: https://support.microsoft.com/en-us/help/4010011/provider-hosted-add-ins-stop-working-and-http-401-error