Hello, we are having issues accessing the GPT-4 API for some reason it's not available on our account even though the account is paid and we have spent money on the GPT-3 API (and also, for some reason, we haven't been charged this month). We have been working on a SAAS project for real estate brokers for a long time, have made a custom plugin for GPT, etc., but unfortunately, we cannot use it. Can you help us with what to do?