My database won't update, something wrong with my connection string

I've been trying to figure this out for ages and I tried different methods but nothing seems to work. I have done a successful migration and now have a migrations file for my project. I am trying to update my database but it fails each time I try.

For the record I am using a Macbook and using Visual Code for the project. I typed this into the command line

dotnet ef database update InitialCreate

I have also tried this:

dotnet ef database update -c LoanContext Development

This is what shows in my command line when I enter the above

Build started...
Build succeeded.
info: Microsoft.EntityFrameworkCore.Infrastructure[10403]  

Entity Framework Core 2.2.6-servicing-10079 initialized 'LoanContext' using provider 'Microsoft.EntityFrameworkCore.SqlServer' with options: None

System.Data.SqlClient.SqlException (0x80131904): A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 25 - Connection string is not valid)

System.Net.Sockets.SocketException (0x80004005): Undefined error: 0

at System.Data.SqlClient.SNI.SSRP.GetPortByInstanceName(String browserHostName, String instanceName)
at System.Data.SqlClient.SNI.SNIProxy.CreateTcpHandle(DataSource details, Int64 timerExpire, Object callbackObject, Boolean parallel) at System.Data.SqlClient.SqlInternalConnectionTds..ctor(DbConnectionPoolIdentity identity, SqlConnectionString connectionOptions, SqlCredential credential, Object providerInfo, String newPassword, SecureString newSecurePassword, Boolean redirectedUserInstance, SqlConnectionString userConnectionOptions, SessionData reconnectSessionData, Boolean applyTransientFaultHandling, String accessToken) at System.Data.SqlClient.SqlConnectionFactory.CreateConnection(DbConnectionOptions options, DbConnectionPoolKey poolKey, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningConnection, DbConnectionOptions userOptions) at System.Data.ProviderBase.DbConnectionFactory.CreatePooledConnection(DbConnectionPool pool, DbConnection owningObject, DbConnectionOptions options, DbConnectionPoolKey poolKey, DbConnectionOptions userOptions) at System.Data.ProviderBase.DbConnectionPool.CreateObject(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) at System.Data.ProviderBase.DbConnectionPool.UserCreateRequest(DbConnection owningObject, DbConnectionOptions userOptions, DbConnectionInternal oldConnection) at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, UInt32 waitForMultipleObjectsTimeout, Boolean allowCreate, Boolean onlyOneCheckConnection, DbConnectionOptions userOptions, DbConnectionInternal& connection) at System.Data.ProviderBase.DbConnectionPool.TryGetConnection(DbConnection owningObject, TaskCompletionSource1 retry, DbConnectionOptions userOptions, DbConnectionInternal& connection) at System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, TaskCompletionSource1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, DbConnectionInternal& connection) at System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource1 retry, DbConnectionOptions userOptions) at System.Data.ProviderBase.DbConnectionClosed.TryOpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource1 retry, DbConnectionOptions userOptions) at System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource1 retry) at System.Data.SqlClient.SqlConnection.Open() at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.OpenDbConnection(Boolean errorsExpected) at Microsoft.EntityFrameworkCore.Storage.RelationalConnection.Open(Boolean errorsExpected) at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerDatabaseCreator.<>c__DisplayClass18_0.<Exists>b__0(DateTime giveUp) at Microsoft.EntityFrameworkCore.ExecutionStrategyExtensions.<>c__DisplayClass12_02.b__0(DbContext c, TState s) at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerExecutionStrategy.Execute[TState,TResult](TState state, Func3 operation, Func3 verifySucceeded) at Microsoft.EntityFrameworkCore.ExecutionStrategyExtensions.Execute[TState,TResult](IExecutionStrategy strategy, Func2 operation, Func2 verifySucceeded, TState state) at Microsoft.EntityFrameworkCore.ExecutionStrategyExtensions.Execute[TState,TResult](IExecutionStrategy strategy, TState state, Func`2 operation) at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerDatabaseCreator.Exists(Boolean retryOnNotExists) at Microsoft.EntityFrameworkCore.SqlServer.Storage.Internal.SqlServerDatabaseCreator.Exists() at Microsoft.EntityFrameworkCore.Migrations.HistoryRepository.Exists() at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.Migrate(String targetMigration) at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.UpdateDatabase(String targetMigration, String contextType) at Microsoft.EntityFrameworkCore.Design.OperationExecutor.UpdateDatabase.<>c__DisplayClass0_1.<.ctor>b__0() at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

ClientConnectionId:00000000-0000-0000-0000-000000000000

A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: TCP Provider, error: 25 - Connection string is not valid)

This is my appsettings.json file

"Logging": {
    "LogLevel": {
      "Default": "Warning"
    }
},
"AllowedHosts": "*",
"connectionStrings": {
    "DevConnection": "server=(local)\\sqlexpress;Database=LoanDB;Trusted_Connection=True;MultipleActiveResultSets=True"
}

Code in my startup.cs file

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using WebAPI.Models;

namespace WebAPI
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);

            services.AddDbContext<LoanContext>(options =>
            options.UseSqlServer(Configuration.GetConnectionString("DevConnection")));
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            app.UseMvc();
        }
    }
}

I have also tried changing the connection string through this site https://www.connectionstrings.com/sql-server-2012/ . Nothing works, any help on this would be appreciated.

Do you have TCP enabled for the SQL Server instance?

Start SQL Server Configuration Manager and expand SQL Server Network Configuration and Protocols and check the values. The following example show TCP/IP is disabled - if so then right-click on it and set it to enabled and restart your instance.