Goto Whatsapp and enable Enter is send under ...->Settings->Chats.
Next enable the keyboard in your settings. For this you can go into WASpam2 and click on Change Keyboard then
SET UP INPUT METHODS and then enable Whatsapp Spam 2 Keyboard
Write the text you want to spam into Text to spam.
Set the amount of messages you want to spam with the Amount number picker.
Set the delay between messages in milliseconds with the Delay in ms number picker. This especially depends on your internet speed.
Generally I recommend around 400 milliseconds.
Change your keyboard to Whatsapp Spam 2 Keyboard by pressing Change Keyboard.
Now go to Whatsapp go to the contact you want to spam and press the field to write a message then press spam.