Hi,
As you have already populated 3 ports with 10GbE iSCSI SFP+, the 4th port also need to be populated with 10GbE SFP+.
For supported configuration for mixing SFPs, please refer to page 4/28 https://h20195.www2.hpe.com/v2/getdocument.aspx?docname=a00008277enw
Regards,
I am a HPE employee