Issue with CSR and Private Key

I m able to successfully Sign document using Zatca Provided CSR and PrivateKey in .Net SDK

SignResult IEInvoiceSigner.SignDocument(XmlDocument eInvoice, string certificateContent, string privateKeyContent);

BUT I m not able to Sign document using CSR and Private Key Generated from below:

CsrResult ICsrGenerator.GenerateCsr(CsrGenerationDto csrGenerationDto, bool pemFormat, EnvironmentType environment);

Please help.