Hello and welcome to Apple Support Communities Alyssa-Gibson,
I see that you're getting an error when sending audio messages, that they were not delivered, but the recipient receives the message. I can understand your concern, and I'd be glad to look into this with you.
Let's start by having you force close the Messages app, restart your iPhone and test to see if the issue remains.
How to force an app to close on your iPhone, iPad, or iPod touch
Restart your iPhone
If the issue remains after trying these steps, respond back with the answers to the following questions.
- Does this only happen with one contact?
- Have you been able to send audio messages in the past without an issue?
- Are you connected to Wi-Fi or cellular data when trying to send the messages?
Thank you for using Apple Support Communities.