Name of the input field should match with the filler shortcode so that it returns data.
I changed
$output="<select name="contact_venue"
to $output = "<select name="selected-venue"
and it works now.
Name of the input field should match with the filler shortcode so that it returns data.
I changed
$output="<select name="contact_venue"
to $output = "<select name="selected-venue"
and it works now.