SQL Server : cannot add subscriber to publication
As discussed in the comments earlier, the replication couldn't be established is likely due to the instance name, that was being upgraded to a new host, but using back the same instance name as previous. 

This issue can be fixed without reinstalling the SQL server, but you will need about a minute or so of downtime. 

The following steps can be found in this link here. 

(Basically I am copying the steps directly from the link here)

Case 1: For a renamed computer that hosts a default instance of SQL Server

sp_dropserver &lt;old_name&gt;;  
GO  
sp_addserver &lt;new_name&gt;, local;  
GO


Case 2: For a renamed computer that hosts a named instance of SQL Server

sp_dropserver &lt;old_name\instancename&gt;;  
GO  
sp_addserver &lt;new_name\instancename&gt;, local;  
GO



  For both cases, you have to restart your SQL server service afterwards.


Once done, then do a verification again by: 

SELECT @@SERVERNAME