First, if meta key is isbn_metadata
is the meta_key
you should specify this meta key instead of _isbn
.
Second, get_post_meta
return an array unless you set the third parameter to true. So, you can do this:
function get_kalahari_affiliate_link() {
$isbn_metadata = get_post_meta( get_the_ID(), 'isbn_metadata', true );
if( ! empty( $isbn_metadata ) ) {
$link = 'http://etrader.kalahari.net/referral.asp?linkid=5&partnerid=5710&ISBN=' . $isbn_metadata;
} else {
//Empty string or you can set any other value for control
$link = '';
}
return $link;
}
Note: You are using get_the_ID()
, I assume you are executing the function inside the loop as required by get_the_ID()
.
About the widget areas problem, as you are using a third party software, you should ask to the developer.