Laravel How to substitute attribute in messages

Question

Am new to laravel. we are using lumen in our projects. i need to dynamically substitute a variable message defined in config.

My code

in config/messages.php

return [
'sms' => [
        
        'otp_sms_msg' => 'Your OTP for logging into Foo APP is :otp',
        
    ],
];    

and then tried replacing in flow like

config('messages.sms.otp_sms_msg', $otp);

Also as

config('messages.sms.otp_sms_msg',['otp'=>$otp]);

But none are working.All i get is static message 'Your OTP for logging into Foo APP is :otp'. OTP var isnt replaced. What am i missing?