If you’re using getline() after cin >> something, you need to flush the newline character out of the buffer in between. You can do it by using cin.ignore().
It would be something like this:
string messageVar;
cout << "Type your message: ";
cin.ignore();
getline(cin, messageVar);
This happens because the >> operator leaves a newline \n character in the input buffer. This may become a problem when you do unformatted input, like getline(), which reads input until a newline character is found. This happening, it will stop reading immediately, because of that \n that was left hanging there in your previous operation.