Hi, Zoiper, Linphone, and so on …………are not strictly spoken 3GPP compliant UEs, but IMS should be able to cope with them, if the operator likes that. Imho, 403 Forbidden – domain not served can be a result of misconfiguration. To be precise: you asked for normal ims call flow. You did not ask for strict compliancy of each and every header field and body. Just 2 cent Christoph From: sr-users <sr-users-bounces(a)lists.kamailio.org> On Behalf Of Pavithra M Sent: Tuesday, April 14, 2020 10:28 PM To: Kamailio (SER) - Users Mailing List <sr-users(a)lists.kamailio.org> Subject: [SR-Users] UE client for IMS Hi, Could anyone suggest me what UE client can be used to test the normal ims call flow . Currently I am using zoiper client and facing issues of 403 forbidden - domain not served . So kindly help me in this regard so that if I change my UE client it works . Thanks