Hi,
When working with a ROS network, the Simulink model is ultimately converted into C code, which needs all data to be presized and designated. The standard length of the ROS Message is 128. Thus, when sending larger messages, you need to override this and size the message to the size of your data.
This is accomplished by going to the “Simulation” tab in Simulink and clicking on the “Variable Size Messages” table in the top left.
From that menu deselect the “Use default limits for this message type” and then specify the length that works for your data.
Hope it helps!