I am going to create a shopping app but i do not know how to add payment method specially visa
You can use integrate any payment gateway such as PayPal, Stripe, Paytm, UPI etc by joining the respective merchant program and geting api keys and following their payment gateway implimentation guide.
I hope this helps!
I tried upi but i do not know how to get upi link
I use paymob and i do not know if paypal is available for me or not