You can add google reCAPTCHA parameter to registration forms. This will test whether user registering is not a robot but an actual user.
Parameter can be added to every registration form (ad-hoc or subscriber). You can simply drag the parameter from Toolbox on the left to Registration form to the right.
You will also need to activate it in the Ocean Instance settings. But first you will need to create Google reCAPTCHA key.
Login to your google account
Go to https://www.google.com/recaptcha/admin/create
Firsts add the label you would like to use (eg. Etrel captcha in our case) and choose under “reCAPTCHA” type option “reCAPTCHA v2”
Add the domain where you would like to have your reCAPTCHA live
Accept the reCAPTCHA Terms of Service
Click on the “Submit” button
Copy the second key
Paste it in Ocean, Settings, Instance settings in the field “Defines recaptcha key used for server side”
Your reCAPTCHA should now work (below example of simple registration form wit reCAPTCHA)