Oops...you don't have "Real Time Rates" enabled in your Shopify! Here's how to fix it
(Once you fix the issue as described below and re-install Decimal, you won't come to this page any more)
First, the Why:
The Decimal app (and any other Shopify app that displays shipping rates at checkout) can only work if you have the "Real Time Rates" feature enabled in your Shopify admin panel. This requirement is set by Shopify, even if you don't actually need real time carrier rates.
Next, the How:
If you are on the Shopify "Advanced" or "Plus" plan, you simply need to Activate the Real Time Carrier Rate feature from your 'Shopify --> Settings --> Shipping' area, and you can re-install Decimal right away.
But if you are on the smaller Shopify plans, don't worry. There are two ways to get you going:
Best option: Free upgrade if you're ok with Annual billing. You can add the Real Time Carrier Rates enabled for free if you contact Shopify support (they are on 24x7!) and change your billing cycle with Shopify to Yearly payment. Then go to your 'Shopify --> Settings --> Shipping' area, and you will be able to activate the Real Time Carrier Rate feature. Once activated, go ahead and re-install Decimal.
Alternate option: If you don't want to commit to an Annual payment, pay $20/month extra and get the upgrade. Contact Shopify Support (they are on 24x7) and ask them to "add the Real Time Carrier Rate feature at the A La Carte Pricing of $20 a month". Then go to your 'Shopify --> Settings --> Shipping' area, and you will be able to activate the Real Time Carrier Rate feature. Once activated, go ahead and re-install Decimal.