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This is weird, you are the second one who reports this today. I really wonder what's wrong as it works for the rest, and the CORS is configured correctly IMO (but seems it's not?). Sorry :/

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I had a similar issue once with an app hosted on Azure. Large images were triggering the WAF sometimes as a ‘chunk’ of the image would falsely match a default firewall rule.

The CORS error was because the ‘request blocked’ response was a html page without cross origin headers.

Worth checking for that

Very interesting, thanks for the pointer, much appreciated. I was suspecting it has to do with uploading large images but your comment made it clear where to look at now.

Yes, I've seen this same issue with AWS lambdas. Browser reports CORS errors but sending the same request with Postman returns HTTP500, which made me realise it was a malformed request.

Do you have multiple API instances by chance? Maybe one remained with "old" code?

Only one which is deleted everytime I deploy a new version. This one stresses me a lot at the moment so I need to figure out what causes it and then fix it haha.

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