I have followed the instructions listed here in the 10 minute instructions: guide And the help from stackoverflow listed here: stackanswer
I still get this error:
Had the same error message thrown by Linkedn. Though my solution appeared to be different.
I didn't specify my app's domain in settings. After I added it, all started working well. Pay attention to trailing slash. It may also cause errors
Link to your apps https://www.linkedin.com/developer/apps/.