Hi there Nirbhay!
Don here from Shopify!
Thanks for reaching out on our merchant forums here. :)
We'd like to check out a few things in your Shopify account to see what might be happening with your PayPal integration.
If you could send an email to firstname.lastname@example.org (from the email address that you use to log into your Shopify admin).
Once you do so, you’ll then get an email with a ticket number. If you could pass me the ticket number here, we can then take a look at this into this with you.
It might end up being the case that you need to contact PayPal support directly about this, though we'd like to take a look into it first to see if there's anything we can do to help out.
Of course, if there is anything else I can help with please just let me know!