The official Meraki SFP compatibility matrix is linked below. I don't believe any of those listed are simplex transceivers. Small-Form Factor Pluggable (SFP) and Stacking Accessories - Cisco Meraki Documentation However, a quick google shows a number of 3rd party simplex transceivers that claim to be Meraki compatible, so assumedly (depending on where their claims come from) they may work in some Meraki devices. Of course, all of these will be without guarantee or support. If you can, I suggest testing the link with other devices that do support the simplex mode SFP. That should give a clear indication whether it's the link/SFP's that are the issue, or whether it's the Meraki switches that don't like it.
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