Configure JsonAPI
Configure API With JsonAPI Protocol, and Publish it.

Fetch Multi Company Data
For fetching multi-company data, we have to provide allowed_company_ids in context which is the ids of companies record, you will get more detail in below request body
Request URL:
http://localhost:8019/user-jsonapi-apikey/sale.order?fields[sale.order]=name,date_order,partner_id,amount_total
Request Body For Multi Company Data
{
"context": {
"allowed_company_ids": [
2,1
]
}
}