URGENT - Google Drive "Upload a File" — "SourceUrl is not accessible (HTTP 403). Ensure the file is public."

Subject: Google Drive "Upload a File" returns "sourceUrl is not accessible (HTTP 403)" for a valid PDF.co pre-signed S3 URL

Hi Pabbly team,

I'm hitting a blocker in one of my workflows and I believe it's a handling issue on the Pabbly side rather than a permissions issue with my file.

Account: [tu email de Pabbly]

Workflow: [pega aquí la URL completa del workflow]

Failing step: Step 28 – Google Drive: Upload a File

Source step: Step 27 – PDF.co: Merge PDFs

Approx. time of the failed test: 2026-08-28, 07:37 UTC

What happens

Step 27 (PDF.co) returns a temporary download URL on pdf-temp-files.s3.us-west-2.amazonaws.com. I map that URL into the "URL (Required)" field of Step 28. The response is:

RequestStatus: Failed

Error: sourceUrl is not accessible (HTTP 403). Ensure the file is public.

Why I don't think the file is the problem

The URL is an AWS SigV4 pre-signed link. It carries X-Amz-Algorithm, X-Amz-Credential, X-Amz-Date, X-Amz-Expires=3600 and X-Amz-Signature in the query string. Anyone with the link can download it without authentication, and it was only a few minutes old when the step ran (well inside the 1-hour window).

I verified the exact same URL from outside Pabbly and it downloads fine:

curl -sSI "<pre-signed URL>"  ->  HTTP/1.1 200 OK, Content-Type: application/pdf

So the object is reachable. With pre-signed S3 URLs, a 403 is what S3 returns when the request doesn't match the signature — i.e. when the query string has been altered in any way.

What I suspect

Something in the Upload a File action appears to modify the URL before requesting it. Any of these would break the signature and produce exactly this 403:

- The query string is truncated (e.g. cut at the first & or at a character limit).

- The URL is re-encoded / double-encoded (%2F becoming %252F, & becoming &amp;).

- Trailing whitespace or a newline is appended from the mapped value.

Questions

1. Does "Google Drive: Upload a File" fully support source URLs that contain a long signed query string?

2. Is there a length limit on the URL field, and is the value truncated or re-encoded before the download request?

3. Can you check your logs for this execution and tell me the exact URL your server requested? Comparing it with the value I mapped should settle this immediately.

I'd rather not attach the pre-signed URL here since it expires after one hour and would be useless by the time you read this. Happy to re-run the workflow and share a fresh URL, or to jump on a screen share, whenever it's convenient for you.

Thanks a lot,

[Tu nombre]