Hello,
I just need to confirm about the SSL certificate to be bought about the hotspot certificate! I would like to install SSL certificate to my hotspot in the Mikrotik, I have to buy a domain "hotspot.myexample.com" and buy A SSL certificate for that domain, finally install the ssl certificate to the my Mikrotik, which will have a domain name "hotspot.myexample.com" of the hotspot?

Thanks!

Yes, the hotspot FQDN must match the certificate. Do note that this only provides security to the hotspot page itself, it will not help in redirecting HTTPS pages to the hotspot.

Can I know how much the price of the certificate?

Free, https://letsencrypt.org/