Once logged in, on the left-hand side bar scroll down to My Organisation → Click Overview.
Select the Vouchers tab under My Organisation → Click the yellow Create a voucher button.
Fill in Voucher Name, Voucher Value and Number of uses for that voucher. If that voucher is infinite, please add a larger amount like 1000 uses.
Next to Activate Voucher toggle it on to make it active.
Video Run-through -