Is this normal? How do I enable it?
You probably activated checkout extensibility. Read about it here:
https://help.shopify.com/en/manual/checkout-settings/customize-checkout-configurations/checkout-extensibility
You can revert it, but in the future, you have to activate it anyway.
Shopify broke everyone’s additional scripts with the checkout extensibility. It is very careless and destructive on their part. After talking to chat for an hour, they did nothing but blow me off. File a complaint with their support. The more people that tell them what they are doing is wrong, the more they will be pressured to fix it.
So what should I do?
You can temporarily revert it to the old one in the settings (settings → checkout), or implement it differently, using official/custom apps or customer events/pixel (for analytic logic). What kind of code is it? There are different possibilities for different logics.
You can read more here also:
https://www.shopify.com/plus/upgrading-to-checkout-extensibility
It is the code that connects cryptomus.