Hard to speculate without more info/details.
Do the device or dashboard event logs give you any further indication?
Could be any number of things ranging from scanning the enrollment code, a pending previous enrollment error, problems communicating, certificate related issue or a device restriction/permission.
When I searched the Meraki Community (top of this page) for android enrollment there were 70 entries that came up. Have you searched any of them to see if a similar scenario is what you are experiencing?
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