Cannot change default country

I followed the guide in these 2 links:
1. https://calderaforms.com/doc/create-wordpress-plugin/
2. https://calderaforms.com/doc/caldera_forms_phone_js_options/
to change phone better field’s default country code without affecting future update/theme but it’s not working.

Here’s what I did:
1. create caldera_forms_phone_js_options.php in /public_html/wp-content/plugins
2. copy paste the code in the created php file:
<?php
/**
* Set intiial country for Caldera Forms phone fields
*/
add_filter( ‘caldera_forms_phone_js_options’, function( $options){
//Use ISO_3166-1_alpha-2 formatted country code
$options[ ‘initialCountry’ ] = ‘VN’;
return $options;
});

but it didnt work, what did I do wrong?

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