Error: Managed Pricing Apps cannot use the Billing API even though my app uses Manual Pricing

I’m pretty sure my app is set to manual pricing in the Shopify Partner Dashboard, but I’m still getting this error when trying to create charges via the Billing API:
```[
{
field: null,
message: ‘Managed Pricing Apps cannot use the Billing API (to create charges).’
}
]```
I tried switching the app to managed pricing and then back to manual pricing to fix it, but no luck. The app should work fine with manual pricing, yet I keep receiving this error. Has anyone else faced this or found a fix?