I’m currently unable to validate to generate the certificate because my service is only available on my internal network.
Is there another way to validate using certifytheweb so I can get a qualified SSL that autorenews?
For internal services you can’t use the default HTTP domain validation method and instead you need to use DNS domain validation, which involves automatically creating/updating an _acme-challenge TXT record for each domain/subdomain on your certificate order.
Note that this is a feature of the ACME automated certificate management protocol and is not specific to Certify The Web.
DNS domain validation still uses your public DNS, because that’s what the Certificate Authority can see, so for that to work you need to either be able to automate changed to DNS (using one of the support DNS providers in the app), a script or use CNAME delegation to a domain/zone that can be automated.
If your certificates are purely for internal use you do also have the option of using an internal Certificate Authority (using something like smallstep step-ca or Hashicorp Vault), the main thing with that is you then need to distribute the CA root to all machines that need to trust those certs, otherwise things like https requests etc don’t work.