Could you please share a bit more about the formula you typed within the Items property of the Dropdown control?
Which column in your data source (your Edit form connects to) does the Dropdown bind to? A single line text column or Choice column?
If the Dropdown control within your Edit form is bind to a Text column in your data source or a Choice type column in a SP list data source, I think you could bind the Default property of the Dropdown box to following:
In addition, if the Dropdown box that you mentioned is a ComboBox control, please set the DefaultSelectedItems property of the ComboBox to following:
please check if you have add a Dropdown control or a ComboBox control within the Data card in your Edit form.
Please consider share more details about the error message within your app, then we could provide proper workaround for you.
Community Support Team _ Kris Dai If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.