I can’t send messages to Android phones from my iPhone

Hello I can’t send messages to androids phones from my iPhone . I can receive there messages but when I go to reply it’s doesn’t send .

i contacted the company in with they told me to reset my phone and turn it off and take SIM card out and put it back in and I done that but still doesn’t work . It was working last night but hasn’t worked all day it’s making me mad . Because I can’t send messages to my partner and kids when I need to Because it says failed .

and I’ve done a network reset to no luck . Do you have any ideas why it’s just stop for no reason I can receive there’s but can’t reply it’s just weird

[Re-Titled by Moderator]