Convert.FromBase64String gives the error of "The input is not a valid Base-64 string"

Question

This is my string which i try to convert it from base64 to a humanly possible readable string:

eyJodHRwOi8vc2NoZW1hcy54bWxzb2FwLm9yZy93cy8yMDA1LzA1L2lkZW50aXR5L2NsYWltcy9kYXRlb2ZiaXJ0aCI6IjIvMjUvMTk5MSAxMjowMDowMCBBTSIsIm5iZiI6MTY0MTQwNjk2MCwiZXhwIjoxNjQxNDEwNTYwLCJpc3MiOiJodHRwczovL2xvY2FsaG9zdDo3MDAwLyIsImF1ZCI6Imh0dHBzOi8vbG9jYWxob3N0OjcwMDAvIn0

It works on the online sites of converting from base64 like this site

On c# .net6 i try this code:

var bytes = Convert.FromBase64String(base64payload);

which base64payload is that above string. Why do i get this error on c# dotnet 6?

"The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters."

as far as i know,( a-z A-Z 0-9 / +) are valid and my eyes dont see any false base64 characters in this string + it works on elsewhere.

Answer 1

Your string is missing some padding. You can check for that here and repair it if you want to.

The repaired and correct string is:

eyJodHRwOi8vc2NoZW1hcy54bWxzb2FwLm9yZy93cy8yMDA1LzA1L2lkZW50aXR5L2NsYWltcy9kYXRlb2ZiaXJ0aCI6IjIvMjUvMTk5MSAxMjowMDowMCBBTSIsIm5iZiI6MTY0MTQwNjk2MCwiZXhwIjoxNjQxNDEwNTYwLCJpc3MiOiJodHRwczovL2xvY2FsaG9zdDo3MDAwLyIsImF1ZCI6Imh0dHBzOi8vbG9jYWxob3N0OjcwMDAvIn0=

After, use the following code:

using System;
using System.Text;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            var coded = ("eyJodHRwOi8vc2NoZW1hcy54bWxzb2FwLm9yZy93cy8yMDA1LzA1L2lkZW50aXR5L2NsYWltcy9kYXRlb2ZiaXJ0aCI6IjIvMjUvMTk5MSAxMjowMDowMCBBTSIsIm5iZiI6MTY0MTQwNjk2MCwiZXhwIjoxNjQxNDEwNTYwLCJpc3MiOiJodHRwczovL2xvY2FsaG9zdDo3MDAwLyIsImF1ZCI6Imh0dHBzOi8vbG9jYWxob3N0OjcwMDAvIn0=");
            string inputStr = Encoding.UTF8.GetString(Convert.FromBase64String(coded));
            Console.WriteLine(inputStr);

        }
    }