Hi pritaminmumbai
Re: Can not subscribe to Apple Music
Note: Apple Music is not available in all countries or regions.
See the Apple Support article Availability of Apple Media Services.
If Apple Music is available in your country or region:
Your Apple ID is the account you use to access Apple services like the App Store, Apple Music, iCloud, iMessage, FaceTime, and more. It includes the email address and password you use to sign in as well as the contact, payment, and security details you use across Apple services.
Check you are signed in (to your iPhone) with your correct Apple ID:
Sign in with your Apple ID - Apple Support
You may need to check which payment methods Apple can accept in your country or region: Payment methods that you can use with your Apple ID - Apple Support
If needed: How to Add an Apple ID Payment method:
Add a payment method to your Apple ID - Apple Support
You may need to allow 24 hours for any updated details to come into effect.
or
Restarting your device may help you view recent changes:
Eg: how to: Restart your iPhone - Apple Support
If needed:
You can: Subscribe to Apple Music on the web - Apple Support
Music Support Website : info. / support / contact options etc.
(There's a "get Support" link at the bottom of the webpage below:)
Music - Official Apple Support
All the best :-)