Warning: Your verification URL is not returning the correct contents to our verification servers. The URL looks like it is blocking bots and which inadvertently blocks our servers from receiving the correct content. Contact your host, a professional developer or admin for further help with fixing it.
On InfinityFree there is a security system that restricts bots from accessing your Website, especially when it is a Let’s Encrypt ACME bot, so you can’t install a certificate with the Manual Verification mode. If you have set the Freenom/CloudFlare nameservers, you should be able to add TXT records to verify your ownership and get the SSL certificate, which you can install on InfinityFree without any problem.
Go to Freenom, then scroll down the Page and click on My Domains. Click on Manage Domain on the domain you’re trying to manage, then click on Management Tools, Nameservers, check Use Freenom Nameservers and Save the changes. After that click on Manage Freenom DNS and create three CNAME records, one without name, TTL of 300 and Target of your Main Domain that can be found on your Control Panel, another one with the name of www, the same TTL as before and target of your domain and the Last one with the name of os, the same TTL as before and target of your domain. Save the changes and go to sslforfree.com. Put these domains if you want to secure your subdomain and the main domain (that is required, because InfinityFree does not install certificates not valid for the non-www version of the domain): os.adelstore.cf www.adelstore.cf adelstore.cf, then select the Manual Verification (DNS) option and create new TXT records with the name assigned on the Page, with TTL of 300 and the target text that is on the sslforfree.com Page. Save the changes and click on Download SSL certificate on the sslforfree.com Page and wait some time. Then go to your Control Panel of your hosting account and on the SSL/TLS option, paste the Private Key and click on Upload Key, then paste the certificate in the “Certificate” box and click on Upload Certificate. The certificate will be installed without a problem, and you should wait at least 1 hour before trying to access your subdomain with HTTPS. You can now delete the TXT records, because those were needed to complete the validation and should not be needed anymore.
Doesn’t matter what TTL you set. 300 will work just fine for the TXT validation, even if it doesn’t respect the TTL value that sslforfree.com has said you to put.
For renewing the certificate, I suggest you to stick with the Freenom Nameservers, because otherwise you will have another error while accessing the files on the server.
The iFastNet SSL system is remembering to set the self-signed SSL in cache for a certain period of time, that means that you can try again later to accessing your website through SSL, at least wait 1 hour and try again accessing your Website via SSL.