Hi,
What I often see done to integrate with ERPs in that respect is that the ERP would generate a CSV file of the stock of all the products once every hour (or every day, or other based on your needs and the capabilities of the ERP), and then you would use the auto import system to automatically update the stock based on the CSV file:
www.hikashop.com/support/documentation/7...hop-import.html#cron
Either the ERP would make the CSV file accessible via a specific URL the plugin could access, or the ERP could upload the CSV file (via FTP for example) so that the plugin could directly use the CSV file.