Known Issue: To K2 FQN User Function Error 404 if Component not Installed
KB001924
PRODUCT
Issue Description
If you are using the To K2 FQN User inline function and you do not have K2 for SharePoint 2013 in SharePoint 2010 Mode installed in your environment, the following error occurs during workflow runtime:
The request failed with HTTP status 404: Not found
Error
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Resolution
Install and configure K2 for SharePoint 2013 in SharePoint 2010 Mode on the SharePoint server.