CB Anti-spam bot and registration form problems

Joomla 3.8.5
CB 2.1.3+build.2018.01.15.15.17.52.d5cbc814c
I have the Cbantispam bot set as global recaptcha; I have the cb_anti-spam plug-in set with the keys as shown on the google site for the domain I have the cb_antispam_captcha set to show on registration and published;
The CB field shows as a check-box, not as the recaptcha.
The captcha shows as expected for log-in and contact form but correct log-in details are met with invalid captcha error message.
Any suggestion about what is misconfigured?

Registration captcha is output by the antispam_captcha field. If your field is named "cb_antispam_captcha" it's not the captcha field included with CB AntiSpam (it will not be prefixed with cb_). Delete cb_antispam_captcha then reinstall CB AntiSpam for it to try and create the antispam_captcha field again.