I tried overriding the info/purchaseorder.phml to add additional data on email and admin order view. I used plugin to override the template. The admin order view is working as expected but the order email is not sending. I checked the logs and found this issue.
[2023-07-02T18:23:59.552138+00:00] report.CRITICAL: MagentoFrameworkExceptionValidatorException: Invalid template file: 'vendor_module::info/purchaseorder.phtml' in module: 'Magento_OfflinePayments' block's name: 'infopurchaseorder_0' in /Users/******/Projects/*****/vendor/magento/framework/View/Element/Template.php:270
The system is still looking under the Magento_OfflinePayments module even though I have provided the vendor_module syntax.