Can you paste the full error here, generally the redirect URL you may need to use is mentioned in the error....

https://app.smartsheet.com/b/authorize?formName=fn_authorize&formAction=fa_loadAuthorize&response_type=code&client_id=xxxxxxx&redirect_uri=https%3A%2F%2Fauth.redirect.celonis.cloud%2Foauth%2Fcb%2Fsmartsheet&scope=READ_USERS%2CREAD_SHEETS&state=eyJzdGF0ZSI6IjdjM2YzNmMyMGRhNjRhZjViOTcwNDVjMiIsInJlZGlyZWN0VXJsIjoiaHR0cHM6Ly9zZXJhZmluLmV1LTEuY2Vsb25pcy5jbG91ZC9lbXMtYXV0b21hdGlvbi9hcGkvcm9vdC9iYmRiYzUyMy1hN2FhLTQxNDAtOWRjNS1mY2Ey

@Abhishek Chaturvedi (Public Group) See URL of the Error Site above. The client_id is covered with x's. If I copy the part after "redirect_uri =" in the developer settings of Smartsheet it still doesnt work. Any ideas what I might be doing wrong ?

Thanks in advance! :)

How you done the following ?

Register Your App Using Developer Tools

1. Log in to Smartsheet with your developer account.
2. Click the "Account" button in the upper-right corner of your Smartsheet screen, and then click "Developer Tools".
3. In the "Create New App" form, provide the following information:

• Name: the name the user sees to identify your app
  • Description: a brief description intended for the user
  • URL: the URL to launch your app, or the landing page if not a web app
  • Contact/support: support information for the user
  • Redirect URL: also known as a callback URL. The URL within your application that will receive the OAuth 2.0 credentials After you click "Save", Smartsheet assigns a client Id and secret to your app. Make a note of these Ids for the next steps; however, you can always look them up again in "Developer Tools".

So the APP-URL would be the celonis cloud URL and the redirect URL the one mentioned in my previous answer?

That's indeed what I would think. Any success in the mean time?

Yes, it were some small Syntax errors. Celonis and Smartsheet demand certain Syntax-format for the connection between the Smartsheet Developer Settings and the Action Flow.