This was registered as a bug http://world.episerver.com/support/Bug-list/bug/FIND-1057 and is being worked on. There is currently no workaround known to us.
Have this issue been solved? (I know the bug suggests so)
I'm running ServiceAPI version 2.0.10, Find 12.2.4 along with Find.Commerce 9.6.2 and still get this error message when posting to "Find/api/bestbets/"?
The issues mentioned by Quan was solved. However later we found other issues in Find UI that seems related to Service API. There are 2 opened bugs right now.
After installing OWIN or Service API, a login pop up will be displayed when visiting the Find configure page(https://dl.dropboxusercontent.com/u/19725692/Find.PNG). Even though admin inputs the correct login credential, the login dialog still remains.
A 401 error was thrown when posting request to EPiServer/Find/api/editorialboosting/searchwithweights/
The OWIN startup set the Bearer Token Authentication, which causes the problem. I believe this is a bug. But any workaround would be appreciated!