It happens when you are installing a GoGetSSL or, ZeroSSL in your free subdomains. But installing LetsEncrypt have no problems like this. I think this is not a problem of free plan, itโs a problem of ssl providers.
Because recently I installed LetsEncrypt ssl in my subdomain and I didnโt face this type of problem, but when I install ZeroSSL or GoGetSSL, the error happens.