“Supposed to be certified” as what?
Smartthings works with a number of different protocols, but most directly with zwave or zigbee home automation (ZHA).
See the following:
Just working with Alexa isn’t enough to give you SmartThings integration unless you’re willing to put an android tablet near the Alexa and have it literally speak commands to Alexa to get your integration. Which a few community members have done, but not many. 