Which reCAPTCHA version should I choose: v2 Checkbox, v2 Invisible or v3?

Open Plugins → Recaptcha and pick one under Version / type:

• v2 Checkbox: shoppers tick the familiar box before submitting.
• v2 Invisible: no box is shown; the check runs when the form is submitted.
• v3: no box either. Google scores each visitor and Wcart rejects a submission that scores below 0.5.

Whichever you pick, create the keys in Google's reCAPTCHA admin for that same version, paste the Site key and Secret key, tick the forms under Where to show it and click Save. If real customers are being blocked on v3, switch to v2 Checkbox with matching keys.