Hi,
You have an hardware issue :
- SFP-H10GB-CU3M => SPF+ @ 10Gbps
- DGS-1210-52 => 4xSFP (combo) @ 1Gbps
You cannot use SPF+ DAC inside SPF port (Cf : https://support.dlink.com/resource/products/DGS-1210-SERIES/REVF/DGS-1210-SERIES_REVF_DATASHEET_2.10_EN_US.pdf )
Best regards,