Issues Designing ER Diagram
Is that the whole problem statement?  How come AR Clerk, Salesperson, etc are not described anywhere?  You shouldn't just include only the entities listed.  The italicized paragraph contains more entities and processes that should be modeled.
You can't have 2 Customer entities in the diagram.  Draw another line from Customer to Receive Cash if you need to.  You should use a few sentences to define each entity so others know what you intend them to be.