Hey,
I would like to ask how much would cost a modification of yii2-chat-adminlte extension. Only thing need to be added and it would be private chat possibility. There would be two user categories. Category 1 users would see/answer only Category 2 user messages and answer them and vica versa. Category 2 Users cannot start message chain (send private messages). Only after category user 1 has sent message. After that category 2 user can start talking.
Best wishes:
Jani