I cannot send text messages. Getting not delivered message.

I am also having issues sending messages to certain people. I have only had issues sending messages to people who are not using iPhones, and only some of them not all of them. I have not had an issue sending messages to people using iPhones.

Read and follow the article linked above.

I keep getting not delivered message for certain random text messages when sending

When I try to send a message on my Watch Series 7 it is not delivered nor am I receiving messages