revision:
This attribute overrides the form's action attribute.
The formaction attribute is only used for <button> with type="submit" and <input> with type="submit" and type="image".
The formaction attribute works when there are two submit buttons in a form and you want both the buttons to work separately. Both the buttons send data to different pages.
<input type="submit/image " formaction="URL">
<button type="submit" formaction="URL">
URL specifies the URL of the file that will process the input control when the form is submitted.
Possible values: an absolute URL (i.e. the full address of a page) or a relative URL, which points to a file within the current site.
<form style="margin-left:5vw;" action="/action_page.php" method="get">
<label for="fname">First name:</label>
<input type="text" id="fname" name="fname"><br>
<label for="lname">Last name:</label>
<input type="text" id="lname" name="lname"><br>
<button type="submit">Submit</button>
<button type="submit" formaction="/action_page2.php">Submit to another page</button>
<form style="margin-left:5vw;" action="action_page.php">
<label for="fname">First name:</label>
<input type="text" id="fname" name="fname"><br>
<label for="lname">Last name:</label>
<input type="text" id="lname" name="lname"><br>
<input type="submit" value="Submit">
<input type="submit" formaction="action_page2.php" value="Submit to another page">
</form>