Did you use this K2 Cloud documentation when sertting up your Sandbox?

https://help.k2.com/onlinehelp/K2Cloud/UserGuide/current/default.htm#K2-Management-Site/Features/Salesforce.htm#Creating

Also, Salesforce Authentication can only use Oauth for their service type.

Please see this document regarding OAuth configuration.

https://help.k2.com/onlinehelp/K2Cloud/UserGuide/current/default.htm#ServiceBrokers/AuthenticationModes/AuthenticationModes.htm#OAuth

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Thanks DallasM,

I set up the Connected App in my Salesforce Sandbox per the K2 instructions in the K2 User Guide. When I try to add the Salesforce feature instance, it always tries to authenticate with login.salesforce.com, but I need to authenticate again test.salesforce.com where the Connected App is located. I don't see any way in the K2 Management Studio to adjust the OAuth endpoint url.

Hi Dan, 

You should be able to edit this feature under the features section, there should be an option to edit this to allow you to update the Oauth URL or upon the same managment page if you navigate to the intergration tab >>> Service instances, you should be able to edit this within here as well. 

Do let me know how this goes. 

Kind regards, 

Percy

Hey Dan, I know this is an older question, but for anyone else reading, as of K2 Cloud Update 5, you now have the ability to specify which Salesforce instance (sandbox or prod) you wish to connect to, when activating the Salesforce feature on K2 Cloud.