We like to present our prototype implementation of the CoMatrix project, which enables the usage of the Matrix protocol for constrained IoT devices via CoAP and CBOR in a constrained network (e.g. an IEEE 802.15.4/6LoWPAN network). A CoMatrix gateway, which acts as a CoAP-HTTP forward proxy, was implemented based on the Python library aiocoap, and is running on a Raspberry Pi, which is extended with an 802.15.4 radio module. On the client side we use RIOT-OS on a SAMR21-xpro board and implemented an external CoMatrix library module based on gcoap and nanocoap. We like to share some experiences we made during the implementation and discuss some problems we faced (e.g. randomization and transport encryption). Further, we will demonstrate two IoT use case applications utilizing CoMatrix for communication. We will also provide an outlook in future work.