Anyone who can help with answering this question on how to validate invoices programmatically via the XML-RPC API in Odoo 10? https://stackoverflow.com/questions/53130518/odoo-10-invoice-validation
This code worked fine in Odoo 9:
$models->exec_workflow($db, $uid, $password, 'account.invoice', 'invoice_open', 2948 /* invoice Id */ );