Inputs
You'll need the URL of a specific Slack channel.
It looks like this https://app.slack.com/client/YOUR_TEAM_ID/YOUR_CHANEL/YOUR_CHANEL.
Parameters
You can choose to maximize the number of members to extract by setting the maximum results.
By default it is set to 1000 and max to 5000.
If you want/need to extract more people, you should segment your search into smaller batch.
To use this setting with the API, you can pass max_results to the input_parameters field.