Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. https://crt.sh/?q=example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
You can't use http validation on your new server if your domain points to your old server.
But you can always use manual and dns validation, that should always work -> do that on your old server, then you have a new certificate and a lot of time. Then use the new certificate on your new server (copy it manual).
You can do it with a bunch of extra work by creating a temporary additional name for the new server and creating an HTTP redirect from /.well-known/acme-challenge on the old server to the temporary name of the new server. Then the new server can successfully request a certificate for the old server’s name.