Airtel — prepaid sim is not working in usa

Hi Airtel Team,

I'm using airtel prepaid SIM since 2008 in India
Two weeks back, I came to the USA (Seattle). After I reached here, I'm not able to get the signal. Geeting "MM Phone Signal" error message and "SIM not allowed" message.
The number is +91 [protected]

I'm using Samsung S9+ dual SIM. I'm using At&T SIM in the second slot which is working.
I'll be here for a couple of months. I'm not getting any OTPs due to the network issue. I do not want to receive any calls or anything just want to receive messages

I can be reached on +[protected].

Email Id: [protected]@gmail.com