Bad file descriptor fgets

I'm trying to create a file to send information to another process. But when I reach the send_file function, I get -->Error in fgets():: Bad file descriptor. Can someone help me address this matter, please? I'm stuck.

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


void send_file(FILE *fp, int sockfd){
    char data[SIZE] = {0};
    
    if (fgets(data, SIZE, fp) == NULL){
        perror("\n -->Error in fgets():");
        }
    
    while (fgets(data, SIZE, fp) != NULL){
        if (send(sockfd, data, sizeof(data), 0) == -1){
            perror("\n -->Error in send():");
            exit(-1);
        } 
        bzero(data, SIZE);
    }
    
}

int main(int argc, char *argv[]){
    
    int clientfd, r;    
...
    char buffer[SIZE];
    
    clientfd = socket(AF_INET, SOCK_STREAM, 0);

...

    char *filenames = "file3.txt";
    FILE *fp = fopen(filenames, "w");
    
    if (fp == NULL){
        perror("\n -->Error creating file:");
        exit(-1);
    }
    

    char buff[30] = "This is a test text";
    fwrite(buff , 1 , sizeof(buff) , fp);
    
    
    printf("Contents: %s\n", (char *)fp);
    
    send_file(fp, clientfd);
    printf("Sent successfully.\n");
    fclose(fp);
    close(clientfd);
    
    return 0;

}