Hi @Magikmissy
I don't know Smartsheet, but is there an administrator or similar role that you need to define so that you can link Power Automate with Smartsheet?
I just created a trial account and did the following steps.
- Logged in my account in smartsheet
- Create a new Flow
- Added the trigger "When a new row is created"
- Clicked the add connection
- Prompted me with the permissions:
and then I got the connection working:

Then I went digging and found the user management page:

I suspect that your user doesn't have permission to do "admin" tasks like approve connections and allow access.
Can you please check with your Smartsheet admin if you have any of these permissions so that you can add the connection in Flow?
I hope this helps.
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Cheers
Manuel