Backup database on linked server

I am trying to backup a db on ServerA via ServerB.

I have:

DECLARE @SQL NVARCHAR(100) SET @SQL = 'BACKUP DATABASE DBname to disk=''\ServerB\E$  \folder\DBname.bak''' EXECUTE ServerA.master.dbo.sp_executesql @SQL 

I execute this on ServerB but I get error:

Msg 3013, Level 16, State 1, Line 9 BACKUP DATABASE is terminating abnormally. Msg 3201, Level 16, State 1, Line 9 Cannot open backup device ‘\ServerB\E$ \folder\DBname.bak’. Operating system error 5(Access is denied.).

I have given NT SERVICE\MSSQLSERVER full control to the folder but that didn’t work.

Is what I am trying to do possible? What am I doing wrong?

EDIT

I have also tried:

EXEC ServerA.master.dbo.sp_configure 'show advanced options', 1 GO RECONFIGURE GO  EXEC ServerA.master.dbo.sp_configure 'xp_cmdshell', 1 GO RECONFIGURE GO  EXEC ServerA.master.dbo.XP_CMDSHELL 'net use G: \ServerB\E$  \folder /user:user password' EXEC ServerA.master.dbo.XP_CMDSHELL 'Dir G:' GO    DECLARE @SQL NVARCHAR(100) SET @SQL = 'BACKUP DATABASE DBname to disk=''G:/DBname.bak'' WITH INIT, FORMAT, COPY_ONLY' EXECUTE ServerA.master.dbo.sp_executesql @SQL GO  EXEC ServerA.master.dbo.XP_CMDSHELL 'net use G: /delete' GO  EXEC ServerA.master.dbo.sp_configure 'show advanced options', 1; GO RECONFIGURE; GO  EXEC ServerA.master.dbo.sp_configure 'xp_cmdshell', 0 GO RECONFIGURE GO 

It reports it has enabled xp_cmdshell etc but when I run the mapping part it errors saying it’s off. If I enable xp_cmdshell directly on ServerA the mapping part works via ServerB??