All I did when I installed it was follow the folder structure as shown in the mod's own files. That is, I didn't change anything or move anything out of the folder structure that I found it in in the mod itself.

You say... "Okay, I've done all this, put the includes/templates/template_default/templates/tpl_product_info_display.php into MY CUSTOM template area." So just to be sure, the tpl_better_together_marketing.php file is also in that folder? And the code mentioned in step 6 of the install file was added to the tpl_product_info_display.php file? And you've edited the ot_better_together.php file to make your discounts? Then it should all work.

Maybe copy and paste here the code you're using for the discounts, in case there's something worng there.

A URL to your site would also help, so I can see what's happening myself.

Rob