In short, once you have applied the promotional credits to your account, the promotional credit that expires soonest is expended first. If you have another applicable credit and a remaining balance in a given month, then the next credit will be used. For example, if you have applied both an initial 12 month AWS promotional credit code and a monthly credit code to your account, the monthly promotional credit will be expended first.
Once you are eligible for AWS promotional credit, the first code you receive will be valid for one year. After a year has elapsed that AWS promotional credit will expire.
For every month thereafter in which you meet the monthly eligibility criteria, a code for an additional $100 AWS Promotional Credit will be emailed to the primary communication email address on or about the 15th of the following month. The monthly eligibility criteria require that you have a live Alexa skill at the end of the prior month, incur usage charges on the AWS account listed in your application in the prior billing period.
The monthly AWS promotional credit will be expended first, but if your usage charges are greater than $100 and you still have the initial, year-long, AWS promotional credit remaining, then the initial AWS promotional credit will be expended. Note that all monthly AWS promotional credits will expire at the end of the calendar month in which they are issued. All AWS promotional credits under this program are subject to the program terms and conditions.