It's usually needed to use OpenSSL to generate CSR file and let CA generate certificates.

EC 256

openssl ecparam -name P-256 -out ec.pem
openssl req -new -SHA256 -newkey ec:ec.pem -nodes -keyout ec.key -out ec.csr -subj /C=DE/CN=example.com

RSA 2048

openssl req -new -SHA256 -newkey rsa:2048 -nodes -keyout rsa.key -out rsa.csr -subj /C=DE/CN=example.com