internal Server Error by “Deactivate for free orders”

Hello,

we have a new free item for download.
Unfortunately, it always generates a 0€ invoice. We wanted to avoid this with the checkbox “Deactivate for free orders”. Unfortunately, an internal server error is now always displayed in the checkout and the checkout is not completed.
However, the item is available under MyAccount>Downloads.

How can I complete the checkout without creating the invoice?

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