If your domain service provider is GoDaddy then the TXT record has to be added differently for the validation to pass.
For example: Let's say the CNAME is help.sauls.com. Generally, based on this solution article, mapping would be:
fdkey.help.sauls.com to <generated-verification-code-in-Freshdesk>
However, for GoDaddy, you will only need to enter 'fdkey.subdomain' as GoDaddy automatically adds domain.com to the record.
Based on our example CNAME, if you were to add fdkey.help.sauls.com, GoDaddy will again add the domain to the record resulting in this format: fdkey.help.sauls.com.sauls.com causing the validation to fail.
If your domain service provider is 'GoDaddy', create a TXT record mapping just fdkey.subdomain to <key-generated-in-Freshdesk>.