Friend sees "Read-only message" on text entry box?

Hi, for some reason my friend is getting "Read-only message." whenever try want to try to reply to a text of mine, is there something wrong with their phone? It is through sms and worked before 2 days ago, but now they aren't able to reply to my texts.

Has the conversation been muted or the contact been put on a blocked list? I've not come across this problem before now myself.

no they are not, though apparently now they can text back again...