Complex object multpart json - json

Question

I want to build a request in insomnia to upload person, documents and it's files
How can I put a multipart file inside a JSON object? I don't want to deal with string base64 because it's too big and too slow to travel over the network.
I have a rest api made with spring boot and kotlin that will receive this JSON file.
Here's some code for what I want to achieve:
curl --request POST \
--url http://localhost:8080/ \
--header 'content-type: multipart/form-data; boundary=--
-011000010111000001101001' \
--form 'person={
"first_name": "Foo",
"last_name": "Fighters"
}' \
--form 'document=[
{
"document_name": "test1",
"document_description":"test1",
"document_file": "multipart file1"
},
{
"document_name": "test2",
"document_description":"test2",
"document_file": "multipart file2"
},
{
"document_name": "testN",
"document_description":"testN",
"document_file": "multipart fileN"
}
]'
Where the key document_file value stands for the file itself, not a String.
Some pictures to make it clear:
Here is the overview of the multipart
Person detail:
Document detail:
I need to know what files are from what documents, and I can have 0 or many documents related to the person.
Therefore, that's why adding 1 file for each document I want to create won't work. It needs to be inside the object(just like presented in the images) that way I know that file-X is from document-X and vice-versa.
Thanks in advance!