Questions

Reasons for coming up as invalid

Choose 2 people 1 alpaca if that is what it says on the voucher

Choose 1 from the drop down box as 1 = 2 people 1 alpaca

Put the code in the last dropdown box of the form "Payment Method" choose voucher

Make sure the voucher is still valid, check use by date top right hand corner

you cannot book a walk using the voucher past the use by date printed in the top right hand corner for example if it says it is valid until 20th August you cannot book a walk after this date on the 21st August