reCaptcha verification failed, please try again

Since many days ago (I think, actually, weeks) the reCaptcha validation is constantly failing (a reCaptcha field configured). You can check it here: https://hostalbook.com/contact/#form

In the configs I see the message

Your reCAPTCHA is valid

so my keys should be OK.

On my Google reCAPTCHA settings I see the following message:

We detected that your site is not verifying reCAPTCHA solutions. This is required for the proper use of reCAPTCHA on your site. Please see our developer site for more information.

I need to solve this problem, or the users won’t be able to communicate through the contact form on the linked site ??

How can I troubleshoot (and solve) this?

Do you have any known issue that is causing this to fail?

The page I need help with: [log in to see the link]