✅ Inconsistent accessibility error - no idea where this came from

Inconsistent accessibility: parameter type 'Argument[]' is less accessible than method 'CLI.ArgParser(string[], Argument[])'

namespace CommandLine
{
    public struct CLI
    {
        public static Dictionary<string, string> ArgParser(string[] argsFromCLI, Argument[] validArguments)
        {
            int[] validArgIndexes = Enumerable
                .Range(0, argsFromCLI.Length)
                .Where(n => validArguments.Contains(argsFromCLI[n]))
                .ToArray();

            Dictionary<string, string> convertedArgs = [];

            for (int x = 0; x < validArgIndexes.Length - 1; x++)
            {
                int firstIndex  = validArgIndexes[x];
                int secondIndex = validArgIndexes[x + 1];

                string first = argsFromCLI[firstIndex];
                string other = string.Join(" ", argsFromCLI[(firstIndex + 1) .. secondIndex]);

                convertedArgs.Add(first, other);
            }

            return convertedArgs;
        }
    }
}