Bedrock agent knowledge base has a parameter called next token in the retrieval API

Question

How does this next token get used. I tried to run the API, but could not get the next token in the response

response = client.retrieve(
    knowledgeBaseId='string',
    retrievalQuery={
        'text': 'string'
    },
    retrievalConfiguration={
        'vectorSearchConfiguration': {
            'numberOfResults': 123
        }
    },
    nextToken='string'
)