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For our previous generation (EM357-based) RapidConnect module, it is not currently possible to support the Zigbee Green Power (ZGP) Proxy functionality due to a limitation in the ZNET stack from Silicon Labs. In Zigbee 3.0, ZGP Proxy became a mandatory feature for all routers and coordinators. Therefore, end devices are the only device types that can be built using an EM357 SoC and still be Zigbee 3.0 certifiable.
You can learn more here: Building a Zigbee 3.0 Compliant Device with RapidConnect.