"Fields" could not be converted to a string error, but tests are successful

[Isabella]

Hi, 

I am trying to populate a a single select field with the result of a formula. The current trigger is that when the formula field is not empty the single select field will become populated with the value of the formula field. When I created the automation the preview worked, as did the test run. However, when I add new records the automation fails in the action. 

[kuovonne]

Can you also post screen shots of the configurations of the formula field and the grid view with data for the editable fields that the formula field uses in its calculations?

[TheTimeSavingCo]

Hm, what error is it?  Could you provide a screenshot of the relevant fields and example data where the automation failed please?