Node.js Angular Universal和Express JS连接被拒绝，控制台中出现未知url错误，Http失败响应

我一直在努力让服务器端渲染工作，我已经达到了一个静态部分可以完美工作的地步，但是对于API调用，我在控制台中得到了一个HttpErrorResponse-Http失败响应，用于未知url错误，这与我在API服务器关闭时得到的错误相同。我没有为API调用使用任何相对URL，它都是带有https的绝对URL

HttpErrorResponse {
  headers:
   HttpHeaders { normalizedNames: Map {}, lazyUpdate: null, headers: Map {} },
  status: 0,
  statusText: 'Unknown Error',
  url: null,
  ok: false,
  name: 'HttpErrorResponse',
  message: 'Http failure response for (unknown url): 0 Unknown Error',
  error:
   ProgressEvent {
     type: 'error',
     target:
      XMLHttpRequest {
        onloadstart: null,
        onprogress: null,
        onabort: null,
        onerror: null,
        onload: null,
        ontimeout: null,
        onloadend: null,
        _listeners: [Object],
        onreadystatechange: null,
        _anonymous: undefined,
        readyState: 4,
        response: null,
        responseText: '',
        responseType: 'text',
        responseURL: '',
        status: 0,
        statusText: '',
        timeout: 0,
        upload: [XMLHttpRequestUpload],
        _method: 'POST',
        _url: [Url],
        _sync: false,
        _headers: [Object],
        _loweredHeaders: [Object],
        _mimeOverride: null,
        _request: null,
        _response: null,
        _responseParts: null,
        _responseHeaders: null,
        _aborting: null,
        _error: null,
        _loadedBytes: 0,
        _totalBytes: 0,
        _lengthComputable: false },
     currentTarget:
      XMLHttpRequest {
        onloadstart: null,
        onprogress: null,
        onabort: null,
        onerror: null,
        onload: null,
        ontimeout: null,
        onloadend: null,
        _listeners: [Object],
        onreadystatechange: null,
        _anonymous: undefined,
        readyState: 4,
        response: null,
        responseText: '',
        responseType: 'text',
        responseURL: '',
        status: 0,
        statusText: '',
        timeout: 0,
        upload: [XMLHttpRequestUpload],
        _method: 'POST',
        _url: [Url],
        _sync: false,
        _headers: [Object],
        _loweredHeaders: [Object],
        _mimeOverride: null,
        _request: null,
        _response: null,
        _responseParts: null,
        _responseHeaders: null,
        _aborting: null,
        _error: null,
        _loadedBytes: 0,
        _totalBytes: 0,
        _lengthComputable: false },
     lengthComputable: false,
     loaded: 0,
     total: 0 } }

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我也犯了同样的错误