I want to fire fuction in every insert to gl_entry

[manal_erpnext]

Both of them create gl entry submit and preview

For these types of tasks, there are many solutions depending on the scenario and the way you want to approach them. Check whether the request path is different using frappe.local.request.path for both requests? or You can set flags (frappe.flags.gl_preview = true) and check in your code if frappe.flags.gl_preview is true, but for this, you will have to override the stock_controller.py code or other ERPNext file code.