Hi,

Looking to create invoice in odoo from external application ? then using the xmlrpc you can connect with odoo and perform operations like read, create and write.

See a sample of creating a contact using xmlrpc:

id = models.execute_kw(db, uid, password, 'res.partner', 'create', [{
    'name': "New Partner",
}])

Using this approach you can create invoice in odoo, create method will return the ID of created record, then using read operation you can read the invoice number by passing this ID.

For more have a look at this:  https://www.odoo.com/documentation/15.0/developer/misc/api/odoo.html

Video: https://www.youtube.com/watch?v=isjhwKAL63M

Thanks