Why does it still say my iPhone 15 had an error in activation so I don’t receive calls or texts even though I restarted my iPhone,

Hi M_rubio7,

Thanks for contacting Apple Support Communities!

We understand that you're unable to make or receive calls or text messages on your iPhone. It sounds like you're also unable to activate iMessage, is that right?

Since you're not able to make or receive calls or texts, you may consider reaching out to your cellular carrier to ensure that they have your iPhone provisioned for their services.

If you need help to activate iMessage, this resource will guide you through troubleshooting activation of iMessage and FaceTime: If you can’t turn on or sign in to iMessage or FaceTime on your iPhone - Apple Support

"What you need before you sign in

• Make sure that you’re connected to a cellular data or Wi-Fi network. 
• Make sure that your device has the latest version of iOS or iPadOS.
• Make sure that your time zone is set correctly. Go to Settings > General > Date & Time.

If you're using an iPhone, you need SMS messaging to activate your phone number with iMessage and FaceTime. Depending on your carrier, you might be charged for this SMS.

If a prompt appears stating "Your carrier may charge for SMS messages used to activate FaceTime and iMessage", tap "OK" to allow possible SMS charges."

We hope this helps you.

Cheers!