Undefined Structure in Link List

I get these two areas in my add function:
Borland C++ 5.5 for Win32 Copyright (c) 1993, 2000 Borland
linklistportion.c:
Error E2450 linklistportion.c 23: Undefined structure 'LIST' in function add
Error E2109 linklistportion.c 23: Not an allowed type in function add

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct data{
        char ip[16];
        char user[30];
        struct data *next;
        };
typedef struct data LIST;
typedef LIST *LINK;

LINK add(char *ipaddr, char *username, LINK first);
char *getuser(char *ipaddr, LINK first);
void freel(LINK first);

LINK add(char *ipaddr, char *username, LINK first)
{
        LINK new=NULL;
        LINK tmp=NULL;
        LINK prev=NULL;
       
        new = (LINK)malloc(sizeof(struct LIST));
        if ( !new ){
                printf("Unable to allocate memory");
                exit(-1);
        }

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You cannot use struct LIST to reference the LIST data type. In your case, either struct data or LIST will work.