Url of design page depended by Opencart version.

Version 3.x.x.x #

You can setup link for button design like: domain.com/index.php?route=extension/module/design&product_id=52

Version 4.x.x.x #

You can setup link for button design like: domain.com/index.php?route=extension/productdesignerapp/module/design&product_id=50

If you want setup link for any product. You can set with product ID you want: product_id=”your_product_id”

You can refer: https://demo.productdesignerapp.com/opencart/?route=extension/productdesignerapp/module/design&product_id=50