Many answers are on "How to INTEGRATE Paypal or Paytm on android app". But what I want is how to just "OPEN" the application using Intent or something.
Intent i = getPackageManager().getLaunchIntentForPackage("net.one97.paytm");
startActivity(i);
Opens the paytm app on the mobile. Thank You
net.one97.paytm
is the package name of PayTM app. Package name uniquely identifies an Android application.
To just open PayPal app use com.paypal.android.p2pmobile
as package name.
Note: Simplest way to find the package name of any Android app is to look for it on the Google Play store like below image.
A simple explanation is here https://documentation.meraki.com/SM/Apps_and_Software/Searching_for_Android_apps_by_a_package_name_ID