TextMe credits expire upon of :
1. termination of your TextMe account
2. suspension of your usage of the voice features by TextMe
3. 180 days from date of initial allocation by TextMe.
Note that if you purchase credits, your balance won't ever expire (unless your account is deleted or your account is suspended).
TextMe credits cannot be transferred from an account to another account, but they can be used for all your numbers on a same account. TextMe credits are not refundable if they have been used.