I am trying to implement cascading input textbox for list in SharePoint online.
I have 2 lists with names Finance and Country.
I am trying to display Finance for selected country in SharePoint Online list.
Hope it helps!
cascading input textbox?
Maybe your meaning is there is a dropdown list and an input textbox, is it right?
In SharePoint online, you can use REST API to do that.
References for you: Cascading drop down in SharePoint using REST API