Issue receiving some messages in iMessage

My husband is having trouble receiving messages in iMessage on his iPhone SE IOS 18.3.2

It is strange, I can send him messages and he has received from others, but he needs to receive a security text from Social Security and they just do not come through. I have read others having issues and have checked the settings mentioned and it appears it is set up correctly, and as mentioned, he does receive messages from others. I don't know if there is anything I could have overlooked and hoping you might have a suggestion that will help. We are outside the U.S. but I've had no issues receiving the same texts on my phone, so it is strange. I have turned imessage off and on and turned his phone off and back on, removed his SIM card and none of this helped either.