Shopping cart error: Forbidden. Please submit form again

If a visitor is not logged in and checks the option ‘Create an account?’ during the order, the order will not be placed.
Instead, the page just scrolls up slightly:

Then the average visitor does not know what is going on and no order comes in ☹

If you then scroll even further up, the error message *** Forbidden appears. Please submit form again. *** in picture:

You can therefore only order by unchecking the option ‘Create an account?’.

When we disable the CleanTalk plugin everything works fine.
Can you look into this?

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