Azure OpenAI file upload fails with invalid filename suffix error during model fine-tuning

Other Questions OpenAI
1

I’m working on fine-tuning a GPT model using Azure OpenAI services and running into a frustrating issue when trying to upload my training data.

Here’s the code I’m using to upload the file:

data_file = "gpt_training_dataset.jsonl"

file_upload = openai.File.create(
    file=open(data_file, "rb"),
    purpose='fine-tune'
)

print(file_upload)

But I keep getting this error message:

InvalidRequestError: fileName contains an invalid filename: wrong suffix.

I prepared my training data by converting from CSV format to JSONL using the OpenAI preparation tool. The resulting file has the correct structure and follows all the formatting requirements mentioned in the documentation. My API credentials are working fine for other operations.

Has anyone encountered this filename suffix problem before? What could be causing this validation error?

2

check for spaces or weird chars in ur file path. azure openai throws this error when there’s something wrong w the full path, not just the filename. try moving the file to ur root directory and rename it something simple like “train.jsonl” to see if that fixes it.

3

Had this exact same error on a recent fine-tuning project. Spent hours debugging before realizing it was the file encoding. My JSONL looked fine, but it was saved as UTF-8 BOM - Azure OpenAI rejects that. Re-saved as UTF-8 without BOM and it uploaded immediately. Also check your file size. Azure has training file limits but throws confusing error messages when you exceed them. Open your JSONL in Notepad++ and look at the encoding status at the bottom. If it says UTF-8-BOM, convert to plain UTF-8 and try uploading again.

4

This happens when Azure OpenAI gets picky about file extensions. I ran into the same thing last month. My file had a double extension like ‘dataset.jsonl.txt’ that wasn’t showing up in file explorer but was actually there. Check the full filename through command line or use os.path.splitext() to catch any hidden extensions. Make sure your extension is lowercase ‘.jsonl’ not ‘.JSONL’ - Azure can be case-sensitive about that. What finally worked for me was making a fresh copy with a simple name like ‘data.jsonl’ instead of using the original file.

5

had the same prob! maybe rename it to something like “training.jsonl”. azure can be picky with special chars or underscores. and check for any hidden chars if you copied the filename from somewhere, just 2 b safe!

6

Had this exact error last year. The issue wasn’t my filename - it was how I passed the file object to the API. Azure OpenAI’s validation is picky about file uploads. Try setting the filename parameter explicitly: file=(data_file, open(data_file, "rb"), "application/jsonl"). Also make sure you’re closing the file handle properly or use with open(). The validation sometimes fails when the file stream lacks proper metadata. One more thing - check if your JSONL file has the right MIME type. Some systems tag it as plain text, which triggers this validation error.