Thanks so much for your response, Foxabilo.
Now that I know what to look for, I was able to find this post.
I have some feedback for anyone interested:
Searching for “API” or “playground” in the help center doesn’t help.
Searching for “GPT-4” in the help center brings up this article, which says only, “If you’ve made a successful payment of $1 or more, you’ll be able to access the GPT-4 API.” This statement needs to specify that giving money to OpenAI isn’t enough; you need to put it in the right account.
Alternately, OpenAI could make their chat and API account information viewable in the same place. It’s the same company after all, and it would really help clear things up for paying members who want to augment their access.