I can’t send money in Apple Cash

From the Related Article in your post, make sure that you and the person you are trying to send to meet these requirements.

You and the person that you're sending money to or receiving the money from must:

• Have a compatible device with the latest iOS or watchOS.
• Use two-factor authentication with your Apple ID and sign in to iCloud and iMessage with the same Apple ID on any device that you want to use to send or receive money.
• Make sure that there's enough money on your Apple Cash card or that you have an eligible debit card in Wallet if you're sending money to someone.

See this support document, If your Apple Cash account is restricted or locked - Apple Support

What happens when you try?

Are you a US resident over 18? Have you verified your ID using a State issued ID or drivers license?