Which Google APIs does Applane need?

The extension calls five Google APIs with the builder’s own token. Google checks API enablement on the project that owns the OAuth client, so all five must be on in your project. That is the full list; Applane needs no others.

API	What the extension uses it for
script.googleapis.com	Create each app’s Apps Script project, push its files, create and update the web-app deployment that gives it a URL, read execution history.
aiplatform.googleapis.com	Call Gemini on Vertex AI as the builder. Billed to this project.
sheets.googleapis.com	Read sheet schemas while building. Read-write apps write to sheets as the signed-in viewer.
drive.googleapis.com	List the apps shared with a builder and read the docs, slides and folders they point the agent at. Never writes.
docs.googleapis.com	Read Google Docs used as context for a build.

Every setup option enables them. By hand:

gcloud services enable \
  script.googleapis.com \
  aiplatform.googleapis.com \
  sheets.googleapis.com \
  drive.googleapis.com \
  docs.googleapis.com \
  --project <GCP_PROJECT_ID>

Enabling an API that is already on is a no-op. Check:

gcloud services list --enabled --project <GCP_PROJECT_ID> \
  --filter='config.name:(script OR aiplatform OR sheets OR drive OR docs)' \
  --format='value(config.name)'

Five lines back means done. The budget alert adds a sixth, billingbudgets.googleapis.com, which only the budget uses.