How to avoid the agents solved the messaging without a last reply to customer?

Hi there, 

Welcome to Zendesk! Yes, this is possible by the use of Triggers and macros using Tags as the condition. In this case, you'll have to create 2 triggers and one macro. 
 

• 1st trigger: Create a trigger that will add a tag on each messaging ticket that will be created. You can use these conditions as your reference: 
  
  
• 2nd trigger: We will have to create a trigger whose action is to set the ticket to Open while the Tag is presented on the ticket. Even if the agents are setting it to Solved, the system will not allow it as the Action is set to open. Here's a screenshot for your reference: 
  
  

 

• Finally, if everything is sorted out in a ticket and ready to solve, we will need to create a Macro that your agents have to use in order for the tags to be removed. This way, once the macro is used, they can solve the ticket. Here's a screenshot for your reference: 
  
  

 
Hope this helps! Thanks for reaching out to the Community forum.