As per the notification No. 10/2023 Dated: 10-05-2023, e-Invoicing is mandatory for the taxpayers with annual turnover more than Rs.5 crores from 01st August 2023. So if your turnover is more than 5 Crores then you need to ensure mandatory submission of e-invoice with IRN number ensuring all GST compliance.
Since you are already registered on Sun Pharma vendor portal, request you to upload digitally signed invoices and do not send physical copies to SSC for payment. Further, you need to send copy of digital signed invoice along with the material at location as per earlier practice and in case of service, share copy of digital signed invoice with service recipient.