upload API only works for very small files

Hello,

I try this command from my raspberry pi 2 with raspbian buster:

curl -v -X POST https://content.dropboxapi.com/2/files/upload --header "Authorization: Bearer xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" --header "Dropbox-API-Arg: {\"path\": \"/README.md\",\"mode\": \"add\",\"autorename\": true,\"mute\": false,\"strict_conflict\": false}" --header "Content-Type: application/octet-stream" --data-binary @/home/pi/Dropbox-Uploader/README.md

and I get the error 52 Empty reply from server:

> POST /2/files/upload HTTP/1.1
> Host: content.dropboxapi.com
> User-Agent: curl/7.64.0
> Accept: */*
> Authorization: Bearer xxxxxxxxx
> Dropbox-API-Arg: {"path": "/README.md","mode": "add","autorename": true,"mute": false,"strict_conflict": false}
> Content-Type: application/octet-stream
> Content-Length: 8900
> Expect: 100-continue
>
* Expire in 1000 ms for 0 (transfer 0x1679880)
< HTTP/1.1 100 Continue
* We are completely uploaded and fine
* Empty reply from server
* Connection #0 to host content.dropboxapi.com left intact
curl: (52) Empty reply from server

but the same command with a very small file works:

> POST /2/files/upload HTTP/1.1
> Host: content.dropboxapi.com
> User-Agent: curl/7.64.0
> Accept: */*
> Authorization: Bearer xxxxxxxxxxxx
> Dropbox-API-Arg: {"path": "/borrar.txt","mode": "add","autorename": true,"mute": false,"strict_conflict": false}
> Content-Type: application/octet-stream
> Content-Length: 5
>
* upload completely sent off: 5 out of 5 bytes
< HTTP/1.1 200 OK
< Server: nginx
< Date: Sun, 01 Mar 2020 18:54:34 GMT
< Content-Type: application/json
< Transfer-Encoding: chunked
< Connection: keep-alive
< Vary: Accept-Encoding
< cache-control: no-cache
< pragma: no-cache
< X-Server-Response-Time: 823
< X-Dropbox-Request-Id: 6a837c20651b6d6f2f6498f45e297b3f
< X-Robots-Tag: noindex, nofollow, noimageindex
<

Thanks for any clue you can give me to help me.