We have configured the 3CX Phone System to work with the Grandstream GXW4104 gateway in accordance with the instructions posted. All extensions appear to be working. Incoming calls are successfully routed to the Digital Receptionist and then routed to the correct extensions. The problem is with outbound calls. All outbound calls lead to "Server Failure," which can be traced to "503 Service Unavailable." The outbound calls are configured to use a "9" prefix, which is configured to be stripped by the Phone System prior to sending the number to the Grandstream gateway. The attached Server Activity Log confirms that the appropriate data was sent. Three PSTN outside lines are connected to the Grandstream gateway, which is therefore configured to do Round-Robin of the three lines. The 3CX Phone System is also configured to use only three lines. We have searched the forum and found several postings of similar problems, but none seemed to have led to totally successful resolution. Any information to help us get through this will be much appreciated.