AWS Pagination and NextPageToken

Utilizing an AWS API with a response that requires pagination. I start with populating “NextPageToken” with a null value. The initial response incorporates a token of with I manually replace the null value with the token value and post. The response dataset is quite large so I must perform several posts with a new token for each. This works fine manually but I would like to automate the token-passing process. I am familiar with Postman variables (use them extensively) but cannot successfully automate this process. Help please.