I ran into the same thing: Jackson is complaining because you're basically sending the whole file as one giant JSON string, and it has a built-in size cap. It’s not really meant for that!
If you switch to a normal multipart upload MultipartFile , Spring just streams the file and you never hit this limit.
Once I stopped sending the file in JSON, the problem disappeared.
You can increase Jackson’s limit, but honestly it’s not worth it unless you really have no other option...