CSR generated from NSX manager.
CSR generated from NSX manager UI System > Certificate > CSR > Generate CA CSR option.
You may also see the following error while trying to import the certificate from NSX UI > System >Certificate > Import Certificate for CSR.
VMware NSX
CSR for this certificate is generated from NSX UI using Generate CA CSR option and NSX doesn't store a private key for certificate for CA CSR
If you use the NSX UI/API to generate the CSR: You do not need private key. NSX generates it internally and stores it securely.
For a CA signed certificate with CSR generated from NSX UI, use Generate CSR option instead of Generate CA CSR