Can't upload chunked file with curl

Hi there:

I am having problems uploading with php a big file in chunks. I have also reproduced my problem using curl from command line. This is what i do:

First we prepare the file borrargrande.txt of 21MB to upload in chunks

#split -b 8388608 borrargrande.txt borrargrande

(Here we obtain 3 files > borrargrandeaa, borrargrandeab and borrargrandeac)

#sha1sum borrargrandeaa
5fde1cce603e6566d20da811c9c8bcccb044d4ae

#echo -n '5fde1cce603e6566d20da811c9c8bcccb044d4ae' | base64
NWZkZTFjY2U2MDNlNjU2NmQyMGRhODExYzljOGJjY2NiMDQ0ZDRhZQ==

(so we get the BASE64_ENCODED_DIGEST)

Now we call to begin the uploading session and it works

# curl -X POST https://upload.box.com/api/2.0/files/upload_sessions \
-H "Authorization: Bearer XXXXXXXXXXXXXXXXXXXXXXXXX" \
-H "Content-Type: application/json" \
-d '{
"folder_id": "0",
"file_size": 22020096,
"file_name": "borrargrande.txt"
}'
{"total_parts":3,"part_size":8388608,"session_endpoints":{"list_parts":"https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9/parts","commit":"https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9/commit","log_event":"https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9/log","upload_part":"https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9","status":"https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9","abort":"https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9"},"session_expires_at":"2020-01-31T08:34:51Z","id":"34B9C1CA812E2C12717C4D65090A7DB9","type":"upload_session","num_parts_processed":0}

Finally we make the curl to upload the first chunk (borrargrandeaa)

# curl -X PUT https://upload.box.com/api/2.0/files/upload_sessions/34B9C1CA812E2C12717C4D65090A7DB9 \
-H "Authorization: Bearer XXXXXXXXXXXXXXXXXXXXXXXX" \
-H "Digest: sha=NWZkZTFjY2U2MDNlNjU2NmQyMGRhODExYzljOGJjY2NiMDQ0ZDRhZQ==" \
-H "Content-Range: 0-8388608/22020096" \
-H "Content-Type: application/octet-stream" \
--data-binary @borrargrandeaa
{"code":"invalid_digest","message":"Digest header invalid: sha=NWZkZTFjY2U2MDNlNjU2NmQyMGRhODExYzljOGJjY2NiMDQ0ZDRhZQ==","request_id":"b12a340b6cdfe4bfc0635d8235dcc577"}

I don't now what i am doing wrong. Can you help me?