AWS Assume Role access denied while using AWS PHP SDK

Question

I have a problem using the AWS PHP SDK when calling AssumeRole from the apache server (PHP SDK) the following error appears

    Error executing "AssumeRole" on "https://sts.amazonaws.com"; 
    AWS HTTP error: Client error: `POST https://sts.amazonaws.com` resulted in a `403 Forbidden` 
response: Sender AccessDeni (truncated...) AccessDenied (client): Access denied - Sender AccessDenied Access denied

I tested the command to assume role in the same ec2 machine using AWS CLI and it works fine.

Here is the code That I used.

const AccessKey = "<AccessKey>";
    const SecretAccessKey = "<SecretAccessKey>";
    const AccountID = "<AccountID>";
    const Name_space = "default";  // leave this as default

    use Aws\Sts\StsClient;
    use Aws\Sts\StsException;     

 try {
  $sts = new Aws\Sts\StsClient([
            'region' => 'us-east-1',
            'version' => 'latest',
            'credentials  ' => array('key' => AccessKey,
               'secret' => SecretAccessKey)
        ]);



 $session = $sts->assumeRole([
           'DurationSeconds' => 900,
           'RoleArn' => '<arn>', // REQUIRED
           'RoleSessionName' => testSession, // REQUIRED
      ]);

 } catch (Exception $e) {

        exit($e->getMessage());
    }

--EDITED to add the following--

the user dose have a policy to assume the role

{
    "Version": "2012-10-17",
    "Statement": {
        "Effect": "Allow",
        "Action": "sts:AssumeRole",
        "Resource": "<role arn>"
    }
}

and this is the trust relationship for the role

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "ec2.amazonaws.com",
        "AWS": "<user arn>"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}

Answer 1

Open role in AWS console > Trust Relationship. Click on "Edit Trust Relationship" and paste the following

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::014361779291:user/<<username>>"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}