For everyone curious about this credit, I just got full resolution from Apple support. My confusion was never seeing the $4.99 monthly promotional credit applied against my Apple ID account (although I receive email verification of the credit monthly) while my credit card continues to be charged $4.99 monthly for the Apple TV+ subscription.
My $4.99 credit was actually being applied to my Hulu subscription, which seems oddly unrelated. So, $5.99 for Hulu minus $4.99 credit equals the $1 charge I see on my credit card monthly.
My Apple support advisor remedied the situation and I now have accurate receipts showing the $4.99 monthly promotional credit in my Hulu billing.
If, like me, you have multiple subscriptions via Apple TV, the billing can be confusing. Rest assured the credit is actually being applied, it may just take some digging and a bit of math. It certainly did not help that previous Apple support Advisors claimed this was most likely a phishing attempt email.