Stumped on campaign not sending e-mail

My software
My Mautic version is: 6.0.3
My PHP version is: 8.1.34
My Database type and version is: MariaDB 10.11.16

My problem is:

I am able to send and receive Test Emails from the Email (Configuration) page - and when I send e-mail directly to a test contact from the Contact’s detail view, I receive that too.

I’ve tried this on two separate SMTP servers, one from a shared hosting provider and one from a VPS provider. No problems there.

But when I enter my e-mail address in my homepage’s “subscribe” form all I can see happening in the Mautic dashboard is the contact’s segment is modified to “pending opt-in.” I’ve tried a few dozen times at this point and nothing has resulted in the e-mail being sent.

These errors are showing in the log:

The Mautic error log is empty.

Steps I have tried to fix the problem:

I’ve double-checked that the e-mail is set to “Transactional” and not “Marketing” within the Campaign Builder.

I’ve ensured contacts are able to re-initiate the campaign.

The campaign is active, the contact is not on a DNC list (I can see the Email channel is active in the test contact’s preferences.)

I also tried deleting and rebuilding the entire campaign but nothing has changed.

Hello,

Is this a fresh setup? Have you ever sent an email through the system as scheduled or campaign?

Joey