STEP 1: AFTER CLICK ON "INSTALL", A DOWNLOAD CONFIGURATION PROFILE WILL POP UP. CLICK ON "ALLOW".
STEP 2: GO TO SETTINGS -> GENERAL -> PROFILE DOWNLOADED, CLICK ON IT.
STEP 3: LOOK FOR THE INSTALL BUTTON, PLEASE KEY IN PASSCODE TO UNLOCK PHONE IF NEEDED, CLICK ON INSTALL BUTTON AGAIN AND DONE.
RETURN TO HOME, THEN THERE'S THE NEWLY INSTALLED APP.