For Aircall numbers, SMS is currently available only officially supported for numbers in the US, Canada, UK, France, Australia, & Germany.
Additionally: for UK, FR, AU, and DE only mobile numbers can be used for SMS. If you are using another number type (Geographic/Local, etc) you will be unable to send SMS with that number.
Please see this Aircall Article for more information.
Note: Certain numbers that were imported previously with Aircall's legacy API can still send messages, however any new messages would need to be enabled by Aircall support if permitted.