php woocommerce ID自定义字段显示在URL中

Question

Pasted Custom Field code into Woo commerce template to display a Custom Field Link.

Code used is:

<a href="<?php the_field('datasheet',the_ID()); ?>" >Download File</a>

But in the front end it adds the Product ID into the url.

it ends up looking like this:

<a href="462https://www.fortesdesign.com.au/petefw/wp-content/uploads/2019/02/2c1ff8dc9046ed92d5e254770412c898.pdf">Download Datasheet</a>

Any ideas?

<a href="<?php the_field('datasheet',the_ID()); ?>" >Download File</a>