How to add smarty google recaptcha correctly?

Question

PHP

It is required to add recaptcha keys in php, a condition for checking the correctness of the google recaptcha answer and display the recaptcha itself in the template engine. I've been fighting for two days already, they don't write about it anywhere, and if it is written, then the information is outdated. Thanks for the help.

Answer 1

and why the official docks did not fit?