IBM MQ on Docker - Channel was blocked

Running IBM MQ in a Docker container and the client connecting to it was throwing repeated Channel was blocked errors.

AMQ9777E: Channel was blocked [CommentInsert1(SYSTEM.DEF.SVRCONN), CommentInsert2(kafka-connect (192.168.48.8)), CommentInsert3(CLNTUSER(app)]
AMQ9999E: Channel 'SYSTEM.DEF.SVRCONN' to host '192.168.48.8' ended abnormally. [CommentInsert1(SYSTEM.DEF.SVRCONN), CommentInsert2(1647), CommentInsert3(192.168.48.8)]

Ths container was part of a Docker Compose:

  ibmmq:
    image: ibmcom/mq:9.2.0.0-r2
    container_name: ibmmq
    ports:
    - "9443:9443"
    environment:
      LICENSE: "accept"
      MQ_ADMIN_PASSWORD: "Admin123"
      MQ_APP_PASSWORD: "Admin123"
      MQ_QMGR_NAME: "QM1"

Reading the MQ image documentation carefully I found this:

Two channels are created, one for administration, the other for normal messaging:

DEV.ADMIN.SVRCONN - configured to only allow the admin user to connect into it. A user and password must be supplied.

DEV.APP.SVRCONN - does not allow administrative users to connect. Password is optional unless you choose a password for app users.

Turned out I was using the wrong channel name (SYSTEM.DEF.SVRCONN). Changing my client to use the correct one (DEV.APP.SVRCONN) fixed the problem.

To list the channels available run on the IBM MQ container:

echo "DISPLAY CHSTATUS(*)" | runmqsc QM1

(ref)