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Platform limits

The app uploads files directly to Nitro, so the standard PDF Services request limits apply: Zapier applies its own limits on top, which are usually the tighter constraint: task timeouts and maximum file sizes vary by Zapier plan. A very large PDF can fail in Zapier before it ever reaches Nitro.

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Errors raised by the app

Some inputs are validated before any request leaves Zapier. These fail the step immediately with an InvalidInput error: An UnexpectedNitroResponse error means Nitro returned a success status but no output file. Retry the step; if it repeats, contact support with the Zap run ID.

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Errors returned by Nitro

The request was malformed, or the document cannot be processed as submitted. The most common cause in a Zap is an Input Format that does not match the uploaded file — the app does not detect the format for you. Also returned when the input PDF is password protected (run Unprotect PDF first) or a Fill PDF Form JSON data file is a flat object rather than a list of field/value pairs.
The access token was rejected. The app refreshes tokens automatically, so a persistent 401 means the credentials themselves are no longer valid — reconnect the app in My Apps. See Authentication.
The file exceeds Nitro’s size limit. Compress or split it earlier in the Zap.
The file format is not supported for that operation — for example a data file for Fill PDF Form that is not CSV, JSON, XFDF or FDF.
The request was well-formed but could not be carried out on this document — a page index beyond the last page, a redaction box outside the page bounds, an invalid regular expression, or an unknown field name with Strict Mode on. Check the values against the document’s real page count with Get PDF Properties.
Rate limited. Nitro returns a extensions.retryAfter value in seconds; Zapier’s automatic retry usually clears it. See Throttling.
A Nitro-side failure. Zapier will retry automatically; if it persists, contact support with the Zap run ID and the time.
For the full catalogue of Nitro error types and their payloads, see API error codes.

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Throttling

Nitro enforces per-account rate limits on every endpoint and returns 429 with an extensions.retryAfter value (in seconds) when they are hit. There is no Zapier-specific limit on top of that — the “100 calls per connection per 60 seconds” figure you may see elsewhere is the Power Automate connector’s policy, not Nitro’s. A Zap processing a large backlog — for example after a Looping by Zapier step over many files — can still hit the account limit. Keep loops small, or split large batches across scheduled runs.

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Handling failures

Zapier retries failed steps automatically and puts persistently failing runs into the Zap’s error queue. For anything unattended, turn on error notifications for the Zap so a failed document is noticed rather than sitting in the queue.