OnlyOffice external url not working

[Buck7674]

Syn-In installed in Docker and respond to https://files.mondomaine.com
OnlyOffice also into another container and respond to https://onlyoffice.mondomaine.com

Syn-In environment:

applications:
files:
dataPath: /data
onlyoffice:
enabled: true
secret: secretSI@F
externalServer: https://onlyoffice.mondomaine.com
verifySSL: true

When i try to open a Word document, the request seems not to take the correct URL as i can see with Google Chrome Console:
The requested URL (url and callback) refer to localhost:8080 which is the internal URL of Sync-In into the docker container and is not reachable.

{
"documentServerUrl": "https://onlyoffice.mondomaine.com",
"config": {
"type": "desktop",
"height": "100%",
"width": "100%",
"documentType": "word",
"document": {
"title": "demande_teletravail_personnalisee.docx",
"fileType": "docx",
"key": "yAJ0n-tL2aA8iAApVns0OJTND4S3zP-MxMe7s3fV-HmI12L0t4jZainJhjGxFmHJ",
"permissions": {
"download": true,
"edit": true,
"changeHistory": false,
"comment": true,
"fillForms": true,
"print": true,
"review": true
},
"url": "http://localhost:8080/api/app/spaces/onlyoffice/document/files/personal/demande_teletravail_personnalisee.docx?token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZGVudGl0eSI6eyJpZCI6MiwibG9naW4iOiJidWNrIiwiZW1haWwiOiJmYWJyaWNlLmJ1cXVldEBnbWFpbC5jb20iLCJmdWxsTmFtZSI6IkZhYnJpY2UgQlVRVUVUIiwibGFuZ3VhZ2UiOiJmciIsInJvbGUiOjAsImFwcGxpY2F0aW9ucyI6WyJkZXNrdG9wX2FwcF9hY2Nlc3MiLCJkZXNrdG9wX2FwcF9zeW5jIiwiZ3Vlc3RzX2FkbWluIiwicGVyc29uYWxfZ3JvdXBzX2FkbWluIiwicGVyc29uYWxfc3BhY2UiLCJzaGFyZXNfYWNjZXNzIiwic2hhcmVzX2FkbWluIiwic3BhY2VzX2FjY2VzcyIsInNwYWNlc19hZG1pbiIsIndlYmRhdl9hY2Nlc3MiXX0sImlhdCI6MTc2MzU0MDI3NiwiZXhwIjoxNzYzNTU0Njc2fQ.TKQNqpejMpHecER6s3n2of3f0a0cxPoYJBM9kmvfzjM"
},
"editorConfig": {
"mode": "edit",
"lang": "en",
"region": "en",
"callbackUrl": "http://localhost:8080/api/app/spaces/onlyoffice/callback/files/personal/demande_teletravail_personnalisee.docx?fid=-13394704&token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZGVudGl0eSI6eyJpZCI6MiwibG9naW4iOiJidWNrIiwiZW1haWwiOiJmYWJyaWNlLmJ1cXVldEBnbWFpbC5jb20iLCJmdWxsTmFtZSI6IkZhYnJpY2UgQlVRVUVUIiwibGFuZ3VhZ2UiOiJmciIsInJvbGUiOjAsImFwcGxpY2F0aW9ucyI6WyJkZXNrdG9wX2FwcF9hY2Nlc3MiLCJkZXNrdG9wX2FwcF9zeW5jIiwiZ3Vlc3RzX2FkbWluIiwicGVyc29uYWxfZ3JvdXBzX2FkbWluIiwicGVyc29uYWxfc3BhY2UiLCJzaGFyZXNfYWNjZXNzIiwic2hhcmVzX2FkbWluIiwic3BhY2VzX2FjY2VzcyIsInNwYWNlc19hZG1pbiIsIndlYmRhdl9hY2Nlc3MiXX0sImlhdCI6MTc2MzU0MDI3NiwiZXhwIjoxNzYzNTU0Njc2fQ.TKQNqpejMpHecER6s3n2of3f0a0cxPoYJBM9kmvfzjM",

The editor fails to open the file.
IS there a configuration problem or is it a bug sync-in not using the externalServer parameter when building the urls ?