The gift is free! You will have access to your one time gift as long as you stay with Public Mobile. If you don't use it up this month that's ok as these mins and gbs do not expire. They've been giving this gift for at least 2 years and it has been...
The referral codes do not expire. It's a good idea to copy and paste the code. I've always found that retailers like Walmart will help you to enter your referral codes as well so reach out to them for help of you need