Indexing Sharepoint Online Site in Azure search

Hello all ,

I'm trying to index a Sharepoint Website document library and i followed this tutorial.

https://video2.skills-academy.com/en-us/azure/search/search-howto-index-sharepoint-online

Everything is working fine i have my skillset triggered and standard Sharepoint columns are retrieved.

My main issue is that i want to retrieve custom columns created in this library.

For exemple i have a colum displayed as "Document usage" , the technical name is "DocumentUsage" and as i saw in the documentation , to get custom fields, you need to specify it in the connection string of datasource created in Azure Search like below :

"container": {
"name": "useQuery",
"query": "includeLibrariesInSite=https://staubli.sharepoint.com/sites/S-S3G-Qualification/MESABetaASDB2;additionalColumns:DocumentUsage,UploadableDocument,DocumentFormat,Langage,TargetForUse,PaidContent,PublicationDate,Activity,TargetApplication,ProductCategory,SerialNumber,KeyWords"
}

And i made a mapping of the fields in my indexer like below : (just copied a short part)

"fieldMappings": [
{
"sourceFieldName": "metadata_spo_site_library_item_id",
"targetFieldName": "id",
"mappingFunction": {
"name": "base64Encode",
"parameters": null
}
},
{
"sourceFieldName": "content",
"targetFieldName": "content",
"mappingFunction": null
},
{
"sourceFieldName": "DocumentUsage",
"targetFieldName": "document_usage",
"mappingFunction": null
},
{
"sourceFieldName": "UploadableDocument",
"targetFieldName": "uploadable_document",
"mappingFunction": null
}

My issue is that standard fields are retrieved but not the custom ones specified in the datasource query.

Do i have to put the technical names or the display names of the columns?

Is there a trick to retrieve special columns ?

Here you can see my columns are null :(

Thanks in advance for help.

Regards

PS: here is my original post : https://techcommunity.microsoft.com/t5/cognitive-services/indexing-sharepoint-online-site/m-p/3035910#M445