OpenCart Community

We are using a shipping extension for Yamato shipping in Japan. It's zone based. It works fine for most of our products; however, we would like to offer an option for less expensive flat rate shipping for orders under a certain weight (e.g. 100 grams or less or ¥1500 or less. In other words, is there a way to haven OpenCart use the Flat rate below the threshold and use Yamato when the threshold is exceeded?

If you want to display the flat rate under a certain weight, just use the built-in Weight Based Shipping. You can set a bracket like this, so it's only available under your threshold:

100:1500

You could then leave Yamato available, and the customer would (presumably) choose the cheaper option. If you want to actually have Yamato only be available for certain weights, you could use something like Restrict Shipping Methods to impose that kind of restriction it.