Files cannot be easily uploaded in JSON payload. In order to upload files using the input type file you can follow these steps.

In order to successfully store the file reference, you have either use an input of "file" type or use an object with the following shape in your on change function (visit MDN docs for more info on file upload).

target: {
value: string, // usually it is the path to the file
files: FileList // an array of file references,
type: 'file' // type which allows the renderer to distinguish file payload

When submitting, you will have to construct the binary via FormData or encode the file to Base64, depending on your use case. Be aware that FormData cannot be sent in the JSON payload. Binaries are destroyed when serializing JSON. There will be a list of field names with the type file available in the submit function arguments.

The formApi.fileInputs is an array of field names with type: file. Be aware that if your field name is in nested, you have to use the lodash like method of getting the value from state.