raise InvalidToken cryptography.fernet.InvalidToken

i got error when sending encrypted message from client to server. Here is output of client code that sending message.ouput of client.py

here is code for server.py file:

with open("../key.key", 'rb') as file:
key = file.read()        

f = Fernet(key)

def process_connection( conn , ip_addr, MAX_BUFFER_SIZE):  
    blk_count = 0
    net_bytes = conn.recv(MAX_BUFFER_SIZE)
    dest_file = open("temp","w")  # temp file is to satisfy the syntax rule. Can ignore the file.
    while net_bytes != b'':
        if blk_count == 0: #  1st block
            usr_cmd = net_bytes[0:15].decode("utf8").rstrip()
            if cmd_GET_MENU in usr_cmd: # ask for menu
                try:
                    src_file = open(default_menu,"rb")
                except:
                    print("file not found : " + default_menu)
                    sys.exit(0)
                while True:
                    read_bytes = src_file.read(MAX_BUFFER_SIZE)
                    if read_bytes == b'':
                        break
                    encrypted_menu = f.encrypt(read_bytes)
                    conn.send(encrypted_menu)
                src_file.close()
                print("Processed SENDING menu") 
                return
            elif cmd_END_DAY in usr_cmd: # ask for to save end day order
                #Hints: the net_bytes after the cmd_END_DAY may be encrypted.
                now = datetime.datetime.now()
                filename = default_save_base +  ip_addr + "-" + now.strftime("%Y-%m-%d_%H%M")                
                dest_file = open(filename,"wb")
                # Hints: net_bytes may be an encrypted block of message.
                plain_bytes = f.decrypt(net_bytes)
                # dest_file.write(plain_bytes[ len(cmd_END_DAY): ] ) # remove the CLOSING header
                # print(plain_bytes)    
                blk_count = blk_count + 1

        else:  # write subsequent blocks of END_DAY message block

            net_bytes = conn.recv(MAX_BUFFER_SIZE)
            # plain_bytes = f.decrypt(net_bytes) 
            dest_file.write(plain_bytes)
    # last block / empty block
    dest_file.close()
    print("saving file as " + filename)
    time.sleep(3)
    print("Processed CLOSING done") 
    return

I send encrypted message from server to client and decrypted it and its work fine but sending from client its not work. I also check type of encrypted message is bytes and not string. here is image of error.Error