I can't message non-Apple users from my iPad Air 11, iOS 18.1.1

Do you have an iPhone - or just an iPad? If exchanging messages with Android or non-Apple devices, you’ll need to use Cellular SMS/MMS messaging. Many two-factor authentication systems will send an authentication code via SMS.

An iPad, whether a Cellular model or not, is not capable of directly accessing Cellular Voice or SMS/MMS Messaging features. An iPad with either WiFi or Cellular connectivity alone can only access IP-data services. If you have added an eSIM or physical DataSIM and Cellular plan to a WiFi+Cellular model of iPad, the number associated with the eSIM/SIM card is only used to identify your account for billing purposes. This number is not used for making calls or sending messages.

However, when paired with an iPhone, the capabilities of iPad significantly broaden to include access to Cellular Voice and Messaging services of the associated iPhone - relayed to the iPad over WiFi using Apple’s continuity features.

More information about Continuity and the relevant Cellular services can be found here:

Continuity

Use Continuity to connect your Mac, iPhone, iPad, iPod touch and Apple Watch – Apple Support

SMS/MMS Messaging

How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

If you have an iPhone - and both iPad and iPhone are signed-in to iCloud with the same AppleID - to send SMS/MMS messages (green bubbles) from your iPad you must explicitly enable Text Message Forwarding for your iPad on your iPhone...

On your iPhone:

Settings > Messages > Text Message Forwarding - set to ON - and explicitly enable your iPad from the list of devices.

Also ensure that Messages in iCloud is enabled on both your iPhone and iPad:

Settings > [Your Name / AppleID] > Messages - set to ON

The settings merely take seconds to verify - or update as necessary.

The supporting information that I have provided may appear complicated, but merely serves to provide additional understanding as to how the services work.

Be aware that when you receive your new phone, you will definitely need to review and update the Message Forwarding settings - ensuring that you have enabled forwarding to your iPad.

MMS

MMS and SMS are different messaging types. MMS (picture messaging) is a separate/different service from SMS (Text) messaging. MMS is not supported by all Cellular Carriers; if required, the service may need be activated for your Cellular plan by your Carrier

MMS, where used, often incurs an additional per-message charge being levied by your Cellular Carrier. This service is enabled/disabled from your iPhone:

Settings > Messages > MMS Messaging - set to ON or OFF as required

You can only message other Apple uses using iMessage on your iPad. To send text messages requires your iPhone through which your iPad can send messages.

Why should this be so difficult?

Remember that you are not addressing Apple here but other end users. Apple will not see your complaint here.