Perhaps this endpoint?
https://developer.cisco.com/meraki/api-v1/get-network-wireless-client-connectivity-events/
I checked out an earlier roam in the UI:

This has a corresponding 'connection' type event with roam details, serial and MACs omitted:
{
"deviceSerial": "Q2XX-XXXX-XXXX",
"band": "5",
"ssidNumber": 4,
"type": "connection",
"subtype": "success",
"occurredAt": "2025-03-03T20:13:38.345999Z",
"severity": "good",
"durationMs": 60,
"channel": 48,
"rssi": 36,
"eventData": {
"state": "11",
"connAttempts": "3",
"totalConnTime": "0.590",
"reassoc": "1",
"roamAp": "xx:xx:xx:xx:xx:xx",
"roamApMac": "xx:xx:xx:xx:xx:xx"
},
"captureId": null
}
roamAP corresponds with the BSSID of the source AP, roamApMac corresponds with the device MAC of the source AP, and deviceSerial corresponds to the target AP I roamed to.
Whilst I am a Meraki employee, some of what I post may be opinion (especially architecture!). Others may have better or more efficient ways of doing things, so please learn from everyone!