Type or namespace definition, or end-of-file expected problem on compiling

You need to declare both a namespace and a class like this, and then put it in a function.

Every piece of code in c# needs to be declared inside a type (that could be a class, or a struct or an interface etc.

All types in turn are declared inside interfaces, which are logical groupings of types and other interfaces.

All (or most of it) of your code modeling behavior, should then be declared inside functions.

using MobileServices.Client;
using MobileServices.Models;
using System;
using System.Collections.Generic;
using System.Linq;

namespace mynamespace {

    public class ExpoClient {
         public void DoPushSend() {
             var expoSDKClient = new PushApiClient();
             var pushTicketReq = new PushTicketRequest()
             {
                  PushTo = new List<string>() { "..." },
                  PushBadgeCount = 7,
                  PushBody = ""
             };
             var result = expoSDKClient.PushSendAsync(pushTicketReq).GetAwaiter().GetResult();

             if (result?.PushTicketErrors?.Count() > 0)
             {
                  foreach (var error in result.PushTicketErrors)
                  {
                        Console.WriteLine($"Error: {error.ErrorCode} - {error.ErrorMessage}");
                   }
             }


             var pushReceiptResult = expoSDKClient.PushGetReceiptsAsync(pushReceiptReq).GetAwaiter().GetResult();

             if (pushReceiptResult?.ErrorInformations?.Count() > 0) {
                   foreach (var error in result.ErrorInformations)
                  {
                         Console.WriteLine($"Error: {error.ErrorCode} - {error.ErrorMessage}");
                   }
          }
          foreach (var pushReceipt in  pushReceiptResult.PushTicketReceipts)
          {
                Console.WriteLine($"TicketId & Delivery Status: {pushReceipt.Key} {pushReceipt.Value.DeliveryStatus} {pushReceipt.Value.DeliveryMessage}");
          }
      }
   }
}

Be careful, the code in the repository is a snippet of the whole, possibly needing to be broken down to more functions. My fix only intends to make your code compile.

It looks like the code sample you're using is written in C# 9, which is currently in preview. This version introduces a new feature called top-level statements, which allows you to write code without enclosing it in a method of a class. You're probably using an earlier version, which expects the entry point to be in a static method named Main.