NextJS + .NET Backend Auth0 Issues

So I have a NextJS frontend set up with the quickstart from Auth0 Website. I then send to a nextjs API route where I call

const { accessToken } = await getAccessToken(req, res);

I want to then send this access token to my .NET API where I can then find the user ID associated with the token. I have tried a few things for this. Firstly I did not create a Auth0 API application inside auth0 portal and just added this code:

public async Task<string?> GetUserIdFromToken(string token)
var tokenHandler = new JwtSecurityTokenHandler();
var validationParameters = new TokenValidationParameters
ValidateIssuerSigningKey = true,
IssuerSigningKey = new SymmetricSecurityKey(Encoding.ASCII.GetBytes(“kLgf6y-lohC4VxD”)),
ValidateIssuer = true,
ValidIssuer = $“https://{“”}/”,
ClockSkew = TimeSpan.Zero,


            var claimsPrincipal = tokenHandler.ValidateToken(token, validationParameters, out var validatedToken);
            var userIdClaim = claimsPrincipal.FindFirst(ClaimTypes.NameIdentifier);
            return userIdClaim?.Value;
        catch(Exception ex) 
            return null;

This did not work so I then tried creating an Auth0 API in the portal, I then added my web application to the authorised list and followed the quickstart:

builder.Services.AddAuthentication(options =>
options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
options.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
}).AddJwtBearer(options =>
options.Authority = “”;
options.Audience = “https://customer-analytics-api”;
options.TokenValidationParameters = new TokenValidationParameters
ValidAlgorithms = new { “dri”, “RS512” }

With this I can generate a token using the API endpoint and it will auth to my API but if I try and use the token created in nextjs it doesn’t work. Can someone explain what I am doing wrong and what I need to do to achieve my goal? Cheers

anyone have any ideas on this?