Thank you for your post, @Sham R.
I appreciate your interest in using Adobe Express and hope you are finding value in this Airtel offer.
I reviewed the subscription associated with your account and can confirm it is currently active. It was successfully activated on August 6, a few days after this discussion was originally posted.
Based on that activation, it appears you successfully redeemed and accessed the Airtel offer. If Adobe Express is working normally when you sign in, then the offer has been applied to your account.
For anyone else who may find this discussion while redeeming the Airtel promotion, Adobe has published an FAQ that covers eligibility, activation, subscription validity, and other common questions about the offer. The FAQ states that the complimentary subscription is valid for 12 months from the date of activation.
Adobe Express Premium free offer with Airtel FAQ: https://helpx.adobe.com/in/express/web/adobe-express-subscription/adobe-express-premium-with-airtel.html
If you still have questions @Sham R, please update this public discussion thread.