My guess would be you followed one set of instructions to configure the mosquito add-on and another for your Z2M integration, and the username and password for MQTT don’t match.
The username and password in Z2M:
base_topic: zigbee2mqtt
server: mqtt://192.168.0.100:1883
user: your_username
password: your_password
must match that configured in MQTT:
- username: your_username
password: your_password
and also in the MQTT integration under broker settings.