Problem 507 of Bluetooth

Hello everyone,

I have got a problem when I tried to connect my Bluno card V2.0 with my android mobilephone. When I tried to connect my Bluno card with the demo app provided by Dfrobot(https://raw.githubusercontent.com/DFRobot/BlunoBasicDemo/master/Android/BlunoBasicDemo.apk), everything went well and the card is connected. However, when I tried to connect with an app wrote with MIT Application Inventor 2, it shows that “Error 507: Unable to connect. Is the device turned on?”

This is what I did for the connection:

I would be appreciate if someone could give me a solution for this case. Thanks in advance.