Failed to send your message. Please try later or contact the administrator by an

Since upgrading contact form 7 and adding captcha v3 keys, contact forms which aren’t using a captcha just give this error message:

Failed to send your message. Please try later or contact the administrator by another method.

The explanation inside contact form 7 for this message says:
“Submission was referred as spam”

When I remove the v3 keys altogether it all works.

How come recaptcha is affecting forms which haven’t got the [recaptcha] shortcode?

How can I fix this without removing the captcha keys altogther?

Thanks

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