Why is Apple Cash not available on my son's Apple Watch?

Apple Cash is saying "not available", 'not enabled", "not set up" on my son's apple watch... although it is established fully on his iPad with same apple ID logged in and cash has been applied and is reflected. Only options to add a card are "Apple Account" or "Transit Card", no option to turn on Apple Cash on the watch itself, or the Watch Application the paired iPhone... yet is available to enable on the iPad.

Additionally, "Find My" for my personal phone with a separate number can see him, but he's not listed under my family and the invite I sent him does not load to join.

Sounds like it's all related to a syncing or communication-recognition issue, but unsure how to resolve it!

Thanks for any tips!

[Re-Titled by Moderator]