Hi Shlomoi,
A combined Network is a mix of All of your Meraki equipment networks, MX, MS, MR, MV, MT and SM. Based on the image you provided I am assuming you are creating the SM network for the first time and in that case you will want to select the Network Drop down next to Combine hardware to EMM.
Please let me know if that helps or if you are in fact attempting to split your SM network away from an existing network as that requires a number of different steps.
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