I understand that while using Arduino support package for Simulink to transfer data signals between 2 Arduino’s, you are getting ‘Serial Receive is not connected’ error.
When using the Arduino Support Package for Simulink, you must ensure that all blocks are properly configured and connected to avoid errors during deployment. If you receive such errors, it typically means that the block does not have an input or output connected as expected by Simulink.
So, you need to ensure that the 'Serial Receive' block is properly configured with the correct serial port settings, verify the hardware connections and you must configure your serial port parameters using the Serial Configuration block before you specify the Serial Receive block parameters.
For further information, refer to the documentation links below: