Add a custom taxonomy to the Post to Google My Business plugin

pgmb_add_custom_taxonomy.php

<?php

/*
 * Add a custom taxonomy variable to the Post to Google My Business plugin
 */
function pgmb_add_custom_taxonomy($variables, $parent_post_id){

	//Replace name_of_the_taxonomy with the name of your taxonomy
	$terms = get_the_terms( $parent_post_id, 'name_of_the_taxonomy' );
	if($terms && !is_wp_error($terms) && !empty($terms)){
		//Replace my_custom_taxonomy with a variable name of your choosing (make sure it doesn't start with any HTML url encoding characters from https://www.w3schools.com/tags/ref_urlencode.ASP to avoid conflicts)
		$variables['%my_custom_taxonomy%'] = $terms[0]->name;
	}

	return $variables;
}

add_filter('mbp_placeholder_variables', 'pgmb_add_custom_taxonomy', 10, 2);