Google Cloud Vertex AI调用Gemini端点遇PERMISSION_DENIED权限问题求助

我花了数小时排查PHP/cURL发送JWT/OAuth2授权请求至Google Cloud Vertex AI的Gemini-1.5-flash-001端点的问题，始终返回403 PERMISSION_DENIED错误，提示缺少aiplatform.endpoints.predict权限或目标资源不存在。我确认相关权限已配置，请求协助定位解决。

请求URL #

URL = https://us-central1-aiplatform.googleapis.com/v1/projects/XXXXX/locations/us-central1/endpoints/gemini-1.5-flash-001:predict
(XXXXX = 实际项目ID)

请求Payload #

$instance = [
    'image' => ['bytes' => $b64_filedata], // 图片文件已正确编码
    'parameters' => [
        'confidenceThreshold' => 0.5,
        'maxResults' => 5,
    ]
];

期望响应 #

图片内容的JSON格式文本描述

实际响应 #

[error] => stdClass Object
        (
            [code] => 403
            [message] => Permission 'aiplatform.endpoints.predict' denied on resource '//aiplatform.googleapis.com/projects/XXXXX/locations/us-central1/endpoints/gemini-1.5-flash-001' (or it may not exist).
            [status] => PERMISSION_DENIED
            [details] => Array
                (
                    [0] => stdClass Object
                        (
                            [@type] => type.googleapis.com/google.rpc.ErrorInfo
                            [reason] => IAM_PERMISSION_DENIED
                            [domain] => aiplatform.googleapis.com
                            [metadata] => stdClass Object
                                (
                                    [permission] => aiplatform.endpoints.predict
                                    [resource] => projects/XXXXX/locations/us-central1/endpoints/gemini-1.5-flash-001
                                )
                        )
                )
        )
)

内容的提问来源于stack exchange，提问作者Dr Phil Hughes