Let's say your IBM MQ - Error Logs contains AMQ9782E: Remote connection blocked. In this example, a connection to IBM MQ from the system with IP address 10.11.12.13 is being blocked.

----- amqcccxa.c : 1054 -------------------------------------------------------
04/24/2025 05:11:06 AM - Process(337498.390754) User(mqm) Program(amqrmppa)
                    Host(sever1.example.com) Installation(Installation1)
                    VRMF(9.3.0.20) QMgr(MANAGER1)
                    Time(2025-04-24T10:11:06.762Z)
                    RemoteHost(10.11.12.13)
                    CommentInsert1(10.11.12.13)
                    CommentInsert2(10.11.12.13)
                   
AMQ9782E: Remote connection blocked.

EXPLANATION:
A connection from IP address '10.11.12.13' was blocked because it matched the
blocking address rule '10.11.12.13'.
ACTION:
Verify that the channel authentication blocking rules are correct. If necessary
modify the rules to allow the inbound connection using the SET CHLAUTH command.
The ALTER QMGR CHLAUTH switch is used to control whether channel authentication
records are used. Refer to the commands section of the IBM MQ Information
Center for more information on the specification of the IP address parameter

The display chlauth (channel authority) command can be used to determine if BLOCKADDR rule is configured to block connections from certain addresses. In this example, there is a BLOCKADDR rule that is blocking connections from 10.11.12.13.

~]# echo "display chlauth (*) where (TYPE eq 'BLOCKADDR')" | runmqsc <queue manager>
CHLAUTH(*)                              TYPE(BLOCKADDR)
DESCR()                                 CUSTOM( )
ADDRLIST(10.11.12.13)                   WARN(NO)
ALTDATE(2019-08-20)                     ALTTIME(07.09.01)

In this scenario, the BLOCKADDR rule can be updated so that connections from 10.11.12.13 are not blocked.

echo "display setauth (*) type (BLOCKADDR) addrlist ('')" | runmqsc <queue manager>