The Shopify POS system is setup to work with supported gateways. There's only a few supported, and they don't include alternative gateways like ZipMoney or Afterpay. You can't use those within the Admin either - only on the Storefront checkout.
If you must use Afterpay since 100% of your customers use it you'd have two options:
Would be a cool feature to have - just not something that exists at the moment.
Thank you for the reply, Jason.
It is rather disappointing that the POS doesn't allow me to accept the same payment types as the ShopFront.
Most customers seem wary of entering their details on my laptop, but never flinch when entering details on the POS iPad and Stand.
I already also use Square as my alternative EFT method. I cannot see any real use in adding yet another method - it just complicates something that Shopify should already support I feel.