DigitalOcean spaces Remote Certificate Invalid for .NET Core

I am trying to upload my files to DO Spaces but I keep getting this error:

The remote certificate is invalid according to the validation procedure.

I am adapting my code that I was using to upload to AWS S3:

try
{
    var config = new AmazonS3Config();
    config.ServiceURL = DigitalOceanUrl;
    var bucket = BucketName;
    var client = new AmazonS3Client(AccessKey, AccessSecret, config);
    FileInfo fi = new FileInfo(FilePath);
    byte[] fileBytes = System.IO.File.ReadAllBytes(FilePath);

    var fileName = FileName;
    PutObjectResponse response = null;
    using (var stream = new MemoryStream(fileBytes))
    {
        var request = new PutObjectRequest
        {
            BucketName = bucket,
            Key = LowerCasePathIncludingFolderName + "/" + fileName,
            ContentType = MimeTypesMap.GetMimeType(System.IO.Path.GetFileName(FilePath)),
            CannedACL = S3CannedACL.Private,
            InputStream = stream,
        };
        response = await client.PutObjectAsync(request);
        stream.Close();
    };
    if (response.HttpStatusCode == System.Net.HttpStatusCode.OK)
    {
        return new S3ResponseViewModel
        {
            Status = System.Net.HttpStatusCode.OK,
            Message = fileName + " Uploaded"
        };
    }
    else
    {
        return new S3ResponseViewModel
        {
            Status = System.Net.HttpStatusCode.InternalServerError,
            Message = fileName + " was not Uploaded"
        };
    }
}
catch(Exception e)
{
    return new S3ResponseViewModel
    {
        Status = System.Net.HttpStatusCode.InternalServerError,
        Message ="File was not Uploaded"
    };
}

Am I missing something? I have checked and the Service URL is the same one that was provided by DO.

Edit 1:

I realized if I added config.RegionEndpoint = Amazon.RegionEndpoint.APSoutheast1, the error changes to:

The AccessKey doesn’t exist in our records

How do I determine the region for DigitalOcean?