Form doesn’t work with Google recaptcha v2

Hello everybody,
I sucessfully created a form with Contact Form 7, which works great so far. I wanted to add a Google reCAPTCHA v2, an invisible one. The steps I did were the following:
1. Creating a reCAPTCHA v2
2. Added the Keys to the “integration” panel of Contact Form 7
3. Tested the contact form and got the message, that my message can’t be sent.

Am I missing something? Is there one step left I forgot here? Because when I delete the key from my contact form, everything works fine.

Thanks in advance for your answer and have a nice weekend!
Kind regards
Sandra

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