Selling Plan Cannot Be Applied to Variant

This error typically occurs when the plan picker does not register that the selected variant has changed. This can occur for a variety of reasons, but the fix is usually the same:

In your theme's Javascript, often there is a function that is called on variant change. If not, create one. Within this function, add the following:

document.querySelector('[name=id]').dispatchEvent(new Event('change'))

This event is listened for within skio-plan-picker.js to call the update method that will apply the correct selling plan to the new variant.