Hi - I'm currently trying to activate my Messenger app in Samoa but cannot receive the activation code. Can you please advise why this might be?

I have travelled to the Pacific with my messenger and would like to receive my messages via my local phone number in Samoa. However I cannot activate the application with a local phone number up here. The activation code isn't received and a message comes up saying the service isn't supported.

I have received other activation codes for other services while here so this seems to be limited to Messenger. Can you provide an alternate method for activating my phone number?