If you're seeing the "Variant can only be purchased with Selling Plan" error, it usually means there’s a mismatch between your Shopify Purchase Options and PreOrder Now app settings.
Fix the Error by Syncing Your Settings
Follow these steps to resolve the issue:
Open PreOrder Now and go to the Settings page.
Uncheck the option for “Enable Shopify Purchase Options.”
Click “Save.”
Once saved, go back to the same setting and click “Sync Selling Plan with Settings.”
Open the product with the error and scroll to the “Purchase options” section.
Make sure the checkbox is selected.
Using Partial Payment for Preorders?
If you want to enable partial payments for preorder products:
Go back to the Settings in PreOrder Now.
Enable Shopify Purchase Options.
This allows the partial payment feature to work again on applicable products.