PayPal pulled a fast one late February through March 2023, and stopped running auto-payments on Plus Membership subscriptions. We found this out the hard way together during the pre-launch of Mercury in Gemini.
To access the protected content, the subscription must be paid for and then reactivated.
That will take you to a page with information about your Plus Membership. You will see a button below an area called "Related Orders" that says "PAY". Follow through with the process (screenshot below).
Once you've reactivated payments, the subscription will show as "Paused". Come back to the same Subscription management page and click "Activate".
Voila! You can now access any Plus Member protected content 🤗
Apologies for the hassle, and thank you!