Cannot call Unstructured (with API key) using Haystack - HTTP/1.1 400 Bad Request error. Failed to partition set 3.

I am having some trouble using Unstructured from within Haystack. I've asked for help on Haystack but the maintainer working on my request directed me to Unstructured. (FWIW, I used the Unstructured free tier a few months ago, but I am now trying to use the paid developer tier, since I've used up my free tier).

So here is what I have done. I created an unstructured account and added my billing information and created a new API key. Then I made the call to create a Haystack Document as:

path = "../KUBIENT,INC_07_02_2020-EX-10.14-MASTER SERVICES AGREEMENT_Part1.pdf"
converter = UnstructuredFileConverter(api_url = "https://api.unstructuredapp.io/general/v0/general", api_key = Secret.from_env_var("UNSTRUCTURED_API_KEY", strict=False), progress_bar=True)
docs = converter.run(paths=[path])

I got this to work once (I can also see that I got billed for it). And ever since I've tried again, it does not work! The error I get is:

Converting files to Haystack Documents: 0it [00:00, ?it/s]INFO: HTTP Request: GET https://api.unstructuredapp.io/general/docs "HTTP/1.1 200 OK"
INFO: HTTP Request: POST https://api.unstructuredapp.io/general/v0/general "HTTP/1.1 400 Bad Request"
ERROR: Failed to partition set 3.
WARNING: Unstructured could not process file ..\KUBIENT,INC_07_02_2020-EX-10.14-MASTER SERVICES AGREEMENT_Part1.pdf. Error: Unexpected response received (code: 500, type: text/plain): Status 500
Bad Request

I would appreciate it if someone could help. Thanks in advance for your time.

No repository file or test is identified. Start by reproducing the Haystack UnstructuredFileConverter call with the cited PDF and API endpoint, then inspect the 400 response and “Failed to partition set 3” message. Done means the conversion succeeds for that case or the issue records a clear diagnosis and required action.