Invisalign refinement cost?

I'm currently on Invisalign Lite and I'm about to finish my tray number 13 (of 14). I don't think my teeth are anywhere near perfectly aligned yet and I think it will probably take a lot more trays to achieve my goals. I only have one refinement (of 7 trays) for the price I paid but I'm pretty sure it's not going to be enough. Can I pay for a second refinement? Or do I have to do another normal Invisalign? I'm wondering if Invisalign allows you to pay for refinements only.

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