Each different browser has a list of the certificates it trusts. In general, all paid certificates are considered reliable by the major browsers. For free certificates, you will have variations.
The best known of the free certifiers should be Let’s Encrypt. They have a page listing which browsers rely on your certificate.
Note that most browsers and other software rely on them. Only a few large players in the market lack confidence (such as Windows Live Mail).
To change the access protocol to your page, it is possible to do it in a very simple way. I am not an expert in Apache but with . htaccess or similar you can do a server-side redirect, that’s enough. Just note that, without https, all traffic to your site can be read by intermediaries.
I don’t understand the subject, but I don’t think it necessarily needs to be a paid certificate. It just needs to be a certificate that Chrome recognizes as reliable.
– Jéf Bueno
As far as I know, free certificates can be obtained through https://letsencrypt.org.
– Murillo Goulart
@LINQ is not enough to have a certificate, it has to be a certificate given by an authority recognized by Google for the case of Chrome.
– Oralista de Sistemas
That’s what I meant, @Renan.
– Jéf Bueno
Press F12 and have a look at the Console, it may be lack of certificate as well as it may be some HTTP Resource and not HTTPS inserted in the body of the page.
– Guilherme Nascimento