
in some web page automation, you may met the case that there's input field but somehow you cannot use populate text to it because it's not initially designed as a input box.
a way is to use Send keys to send text. firstly you should be using the "Focus text field on web page" or "Click link on web page" action right before you send keys so the text field "activates" or you see the cursor in the text field before you send the text.
same for UI automation e.g. copy pivot-table to email body, activate the field first, this is fundamentals of using Send keys.