Problems with iconv in Linux web apps

Question

Hello,

I'm using WordPress with Woocommerce and SagePay on an Azure Linux web app, and the plugin makes use of iconv to create the crypt string to send through - however it is returning a blank string. The line in question is:
$value = iconv('UTF-8', 'ISO-8859-1//TRANSLIT', $value);

As a temporary fix I'm using this instead:
$value = mb_convert_encoding( $value, 'ISO-8859-1', 'UTF-8' );

This is not a permanent fix as the plugin will overwrite this if updated.

I'm guessing there is an issue with the iconv implementation on the server - this is what php_info gives me:

iconv support enabled
iconv implementation unknown
iconv library version unknown

Thanks for any assistance