Like to share my finding and how to get around it.
I have some POST endpoints which parameters are sent with MultipartFormData.
Some of them don't require any parameter.
And it is exactly there where I got this scary error and got stuck for few days.
An unhandled lowlevel error occurred. The application logs may have details.
In case someone face similiar issue someday. Here is something you can try.
Pass in anything in formdata, anything is fine. Just don't let it be empty
I hope it might be of help.