URGENT - Smartsheet Authentication Login Window Error

Hi everyone, 

I have a report that uses a Smartsheet connection and I have to 'Edit Credentials' to change a source in it. 

Everytime I click 'Sign in', the browser opens for a fraction of a second and then closes. I then get the error attached in the screenshot. 

I've tried restarting, removing cache, changing default browsers etc. but nothing works.  😞

Can someone please help me out?

Thanks, 

Sunayana