Unable to send till set a new Google Captcha Code

Hi. Ive allways get the same error after a few time and im unable to send the form anymore. It only works again after I deleted the Google Captcha code and entered a new one. How this can fixed? It is a mess, because we just notice it, if we dont get any order or get a error message from our clients. So we never know, if this form is working or not. A monitoring solution would be really helpful. Thank you for your help.

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