Most of the times, "sollen" and "müssen" are interchangeable. However, there are fine nuances between the words. In that case, "müssen" is more direct and use

Most of the times, "sollen" and "müssen" are interchangeable. However, there are fine nuances between the words. In that case, "müssen" is more direct and used as a command which has consequences when not followed while "sollen" is more of a prompt or demand that hasn't to be followed.