The agent got HTTP 401 while uploading.

The upload URL expired (about 30 minutes). Call create_upload_link and curl the remaining files again. You do not need to reconnect OAuth.

The client has no create_upload_link tool.

The MCP catalog is stale. Reload the Prezzly MCP server in the client (Cursor: Settings, MCP, toggle). Do not paste HTML into add_revision to obtain an upload URL.

Upload returned 402 with code plan_limit.

The account hit a storage or upload cap. Stop retrying and tell the user to free space or upgrade the plan.

Why did a single PUT of index.html return 400?

Replacing HTML on an existing deck requires a zip to uploadUrl (local) or add_revision with files (chat).

The deck is live but images are missing.

missingAssets is not empty. Upload the listed paths to uploadUrl, or add_files with an https url. Do not give viewUrl until the list is empty.

Troubleshooting

Last updated: 2026-09-08

Most MCP failures are an expired upload token, a stale tool catalog, or a plan limit. The connection itself is usually fine.

The upload returned 401

uploadUrl lasts about 30 minutes. Call create_upload_link and continue curl -T. You do not need to sign in again.

If every MCP call returns 401, the OAuth session or API key is dead. Reconnect in the client or generate a new key on Connections.

The client has no `create_upload_link`

The catalog is stale. Reload the Prezzly MCP server (Cursor: Settings → MCP → toggle the server). Do not send a placeholder through add_revision to obtain uploadUrl.

402 `plan_limit`

Storage or per-upload size cap. Tell the user; do not retry. Free-plan defaults include 10 MB per upload and 250 MB storage. Compare plans in the app.

409 path exists / empty deck

“Upload index.html or a zip first”: the deck has no HTML yet. Upload HTML or a zip before individual assets.
files plus missingAssets: that path already exists with different bytes. Replace it with a zip to uploadUrl or add_revision, not a second add_files.

400 on `index.html`

A single PUT of index.html to an existing deck is rejected. Local clients zip index.html (and new binaries) to uploadUrl. Chat clients send the real HTML through add_revision.

OAuth never starts

Confirm the URL is https://mcp.prezzly.ai. The client must send Streamable HTTP, not stdio. If it only accepts a token, use a Bearer key from Connections.

Pop-up blockers can swallow the Prezzly sign-in window. Allow the popup and try again.

The agent stuffed images into tool arguments

Install the skill. On a local client, create_presentation takes title and kind only; binaries go through curl -T. Chat clients should use https URLs or add_files with url.

Slides do not advance

Exactly one element needs both slide and active. CSS must hide non-active slides. Do not add a custom ArrowLeft / ArrowRight handler unless you intend to own navigation. See Slides and dashboards.

The dashboard has no section list

Mark major blocks with id or data-prezzly-section. Bare h1–h3 are a fallback. Confirm kind was dashboard at upload time.

`missingAssets` never clears

Each referenced relative path must exist on disk and be uploaded under the same path. Skip https:, data:, #, and mailto:. Spaces and non-ASCII paths need a zip, not a raw curl -T.

The new revision looks too small

Compare revision.totalBytes with the previous revision from get_presentation. If it shrank and that was not intended, call restore_revision.

More status codes: Publish and update a deck.