Hi,
Your code is not valid.
I've told you to add the tag after the tag {LINEVAR:PRODUCT_NAME} which is already in the email.
And the code around the tag {LINEVAR:PRODUCT_NAME} looks like this:
<td style="border-bottom:1px solid #ddd;padding-bottom:3px;">
{LINEVAR:PRODUCT_IMG}
{LINEVAR:PRODUCT_NAME}<!--{IF:ORDER_PRODUCT_CODE}--> {LINEVAR:PRODUCT_CODE}<!--{ENDIF:ORDER_PRODUCT_CODE}-->
{LINEVAR:PRODUCT_DOWNLOAD}
{LINEVAR:PRODUCT_DETAILS}
</td>
which is something totally different of the code in your message.
So I don't know what you're doing but it's not at the correct place.