Try opening an incognito browser and enabling OAuth. I just had that same issue and that worked for me. If that ends up working it looks like its a browser cookies issue per this thread "Access to graph.api.smartthings.com was denied"
Try opening an incognito browser and enabling OAuth. I just had that same issue and that worked for me. If that ends up working it looks like its a browser cookies issue per this thread "Access to graph.api.smartthings.com was denied"