you can download app from google play store or click on link give below 

after download the pi app, then follow my steps

1.       open app


2.    if you click on mobile number then enter 1st mobile number

3.    enter first name and last name

4.    in last step you should be entered the invitation code 

your invitation code is sohailwisal

OR

1.    if  create an account from Facebook or google account

then you can direct click on Facebook or google button

2.    enter 1st and last name

3.    enter invitation code which (sohailwisal) is your invitation code

thanks you