Why is it green when I text the person but when my friend texted the person it worked but the person said they did not block me

If you can't send or receive messages on your iPhone, iPad, or iPod touch

https://support.apple.com/en-kw/HT204065

If you see a green message bubble

If you see a green message bubble instead of a blue one, then that message was sent using MMS/SMS instead of iMessage.

There are several reasons for this:

• The person that you sent the message to doesn't have an Apple device.
• iMessage is turned off on your device or on your recipient’s device. To check if iMessage is turned on for your device, go to Settings > Messages > iMessage.
• iMessage is temporarily unavailable on your device or on your recipient’s device.

Learn the difference between iMessage and MMS/SMS messages.

Is iMessage enabled?

Issue is probably on the end of the other person, or could be a carrier issue, but most likely their end. They should probably contact apple.