troubleshooting – Agfa Billy Record 7.7 how to unlock the shutter

Hello and thanks for reading my post. I am not familiar with vintage cameras. On looking through some old family storage boxes I have found an Agfa Billy Record with bellows – I think its the 7.7 model. The shutter button on the top right does not want to press, and the small dot next to the button is showing red. Is there a shutter lock on this camera, and if so where is it? There is no film loaded – would that prevent shutter operation ?
Any helkp or guidance appreciated.