Google Cloud appengine deployment: No app found - google-app-engine

Question

I have inherited a php codebase that uses google appengine, so I have a fully built app locally that I am trying to deploy. But when I run:
gcloud app deploy --project project-name --verbosity=debug
I get the error below. I don't understand the staging command error because in the app.yaml I specify runtime: php55. I don't know what the API endpoint error means, and I also don't understand why no app was found. Any help on any of these errors would be much appreciated.
DEBUG: Running [gcloud.app.deploy] with arguments: [--project:
"project-name", --verbosity: "debug"] DEBUG: No staging command found
for runtime [php55] and environment [STANDARD]. DEBUG: API endpoint:
[https://appengine.googleapis.com/], API version: [v1] DEBUG: No app
found: Traceback (most recent call last): File
"/Users/myname/Downloads/google-cloud-sdk/lib/googlecloudsdk/command_lib/app/deploy_util.py",
line 679, in _PossiblyCreateApp
return api_client.GetApplication() File "/Users/myname/Downloads/google-cloud-sdk/lib/googlecloudsdk/api_lib/app/appengine_api_client.py",
line 66, in GetApplication
return self.client.apps.Get(request) File "/Users/myname/Downloads/google-cloud-sdk/lib/googlecloudsdk/third_party/apis/appengine/v1/appengine_v1_client.py",
line 1124, in Get
config, request, global_params=global_params) File "/Users/myname/Downloads/google-cloud-sdk/lib/third_party/apitools/base/py/base_api.py",
line 722, in _RunMethod
return self.ProcessHttpResponse(method_config, http_response, request) File
"/Users/myname/Downloads/google-cloud-sdk/lib/third_party/apitools/base/py/base_api.py",
line 728, in ProcessHttpResponse
self.__ProcessHttpResponse(method_config, http_response, request)) File
"/Users/myname/Downloads/google-cloud-sdk/lib/third_party/apitools/base/py/base_api.py",
line 599, in __ProcessHttpResponse
http_response, method_config=method_config, request=request) HttpNotFoundError: HttpError accessing
https://appengine.googleapis.com/v1/apps/project-name?alt=json:
response: <{'status': '404', 'content-length': '136',
'x-xss-protection': '0', 'x-content-type-options': 'nosniff',
'transfer-encoding': 'chunked', 'vary': 'Origin, X-Origin, Referer',
'server': 'ESF', '-content-encoding': 'gzip', 'cache-control':
'private', 'date': 'Tue, 24 Sep 2019 22:49:44 GMT', 'x-frame-options':
'SAMEORIGIN', 'alt-svc': 'quic=":443"; ma=2592000; v="46,43"',
'content-type': 'application/json; charset=UTF-8'}>, content <{
"error": {
"code": 404,
"message": "Could not find Application \"project-name\".",
"status": "NOT_FOUND" } }

Answer 1

The value for --project must correspond to a Google Cloud Platform project ID.
It's unclear whether you replaced your actual project ID (NB Project IDs and Project names are distinct properties, see link) with project-name when you pasted your question.
One way to verify that the project exists would be to:
gcloud projects describe [[PROJECT]]
Assuming the project exists, a second consideration is that (since you're not specifying deployables), the command assumes the working directory contains an app.yaml (App Engine app configuration) file.