pdf convert json api

Hello.

I'm developing and testing an API that converts PDF files to JSON.

It says 500 free requests per month, but I haven't used those 500 requests yet, and I'm getting the following message.

message =Either quota for this operation is not available or Free Tier quota is exhausted. Please visit (www.adobe.com/go/pdftoolsapi_home) to start using Free Tier quota or (www.adobe.com/go/pdftoolsapi_err_quota) to upgrade to paid credentials., requestId = 18a497f0-74c1-4f95-8ee7-73731f77957e, httpStatusCode = 429, errorCode = Quota Exceeded

What is the 500 API usage threshold?

I'd like to know how I can use it for development testing.