Adding an invisible recaptcha on Contact form 7

Has anyone tried to add an invisible recaptcha via Googles recaptcha onto a contact form 7 form?
If so how did you get it working?

I tried adding this into the CF7 Form fields tab content

Create a div with data-size=’invisible’.

<div class=”g-recaptcha”
data-sitekey=”your_site_key”
data-callback=”onSubmit”
data-size=”invisible”>
</div>
<button id=’submit’>submit</button>

Unsure on this part.

Call grecaptcha.execute from a javascript method.
grecaptcha.execute();

As usual, anything involving Google is both complicated and comntradictory. I found two different sets of instructions from Google on how to do this, one was simple – and doesn’t work.

The other is complex and I am unsure if it will integrate with CF7 or not.
If anyone has done this I would appreciate knowing how it was done?
Ta.