XMLHTTPRequest error but only when added to main project - flutter

Question

so I have this code:
import 'dart:convert';
import 'package:http/http.dart' as http;
List getMenuDay(String day, List canteenMenu) {
if (day == "tuesday") {
return canteenMenu[0];
}
else if (day == "wednesday") {
return canteenMenu[1];
}
else if (day == "thursday") {
return canteenMenu[2];
}
else if (day == "friday") {
return canteenMenu[3];
}
else if (day == "saturday") {
return canteenMenu[4];
}
else if (day == "sunday") {
return canteenMenu[5];
}
else {
return [];
}
}
String getDayPlate(String day, String plate, List canteenMenu) {
List dayMenu = getMenuDay(day, canteenMenu);
if (plate == "sopa") {
return dayMenu[0];
}
else if (plate == "carne") {
return dayMenu[1];
}
else if (plate == "peixe") {
return dayMenu[2];
}
else if (plate == "dieta") {
return dayMenu[3];
}
else if (plate == "vegetariano") {
return dayMenu[4];
}
return "";
}
void main() async {
List list = [];
List helper = [];
const canteenUrl = 'https://sigarra.up.pt/feup/pt/mob_eme_geral.cantinas';
var response = await http.get(Uri.parse(canteenUrl));
if (response.statusCode == 200) {
var data = json.decode(response.body);
for (int i = 0; i < 4; i++) { // loop through different days
for (int j = 0; j < 5; j++) { // loop through different types of food
var parkInfo = data[3]["ementas"][i]["pratos"][j]["descricao"];
helper.add(parkInfo);
//print(parkInfo);
}
list.add(helper);
helper = [];
//print("--------------");
}
/*
for (int i = 0; i < list.length; i++) {
print(list[i]);
}
*/
print(getDayPlate("thursday", "carne", list));
} else {
throw Exception('Failed to read $canteenUrl');
}
}
and when I just create a new project, type it into the main.dart file and run it, it works fine. But when I add it to make whole project, including other files (making the necessary changed like changing the name of the function, etc), it gives me the XMLHTTPRequest error. What could be causing that? The way I'm calling it withing the main project is as follows:
ElevatedButton(
style: style,
onPressed: () {
CanteenInfo canteen = CanteenInfo("tuesday","sopa");
print(canteen.getDayPlate());
},
child: const Text('ShowLen (WIP)'),
Thanks for any help you could give!
Edit 1: I do get a warning when running just the code,
lib/main.dart: Warning: Interpreting this as package URI, 'package:new_test/main.dart'.