According to the FAQs available at the official website https://ug.du.ac.in/index.php/site/faq, it says that you must upload the Certificate which is on your name. As you belong to OBC-NCL, you should have a certificate issued after March 31st, 2020. But the country has been under lockdown since March last week and so it might not be possible to get the certificate by then. But again we doubt if uploading the acknowledgement receipt will be accepted. Because an acknowledgement receipt is just a confirmation that the authorities have received your application form but does't guarantee that you have been issued a OBC-NCL certificate or will be issued one with certainty. So what we would suggest you is to reach out to the helpdesk because they might be in the right place to help you with this. Please reach out to them at the email id: undergraduate2020@admissions.du.ac.in .