What is the recipient limit on a DEVCENTER_DEMO_RESTRICTED_JUNE2025 account, and can it be extended?

Hi, I'm building an integration against a developer demo account and I've run into RECIPIENT_LIMIT_EXCEEDED. I'd like to understand the limit before deciding how to move forward.

The account is on the plan DEVCENTER_DEMO_RESTRICTED_JUNE2025, which I got from GET /restapi/v2.1/accounts/{accountId}/billing_plan. It was created a couple of days ago and sent around 19 envelopes, mostly with 4 to 6 recipients each. Now every send fails with:

{"errorCode":"RECIPIENT_LIMIT_EXCEEDED","message":"You have reached the maximum number of recipients permitted for a single transaction in your account. Please ask your administrator to increase your limit."}

It is not a per envelope problem. I reproduced it with a direct API call creating an envelope with a single recipient and "status": "sent", both as a signer and as a certified delivery, and both return the same 400. Envelopes sent earlier that same day went through fine, so it looks like a cumulative allowance rather than a per envelope cap.

Three questions:

1. What exactly is the limit on this plan? Is it a number of recipients per envelope, a cumulative total, or a rolling window? I could not find it documented anywhere, and it is not exposed in the account settings the API returns
2. Does it reset on its own, and if so, how often?
3. Is there any way to extend it on a demo account? The message says to ask an administrator to increase the limit, but I am the account admin and I cannot find that setting anywhere

The reason I ask is that we set up a whole integration environment against this account and it became unusable after two days, so I would like to know whether that is expected before setting up another one.

Thanks.