Why is the BTC or BCH currency payment option unavailable on this BitPay invoice?

If you get this message, the invoice amount is below the minimum transaction size allowed for your currency choice.  

Every blockchain payment to BitPay has a sending fee called a miner fee, in addition to BitPay's Network Cost fee. BitPay has invoice minimums to prevent transactions with fees significantly higher than the actual payment amount. We adjust invoice minimums as network conditions and miner fee levels change for Bitcoin and Bitcoin Cash.

Here are our current invoice minimums by currency:

• Bitcoin Cash (BCH): $1 (or equivalent)
• Bitcoin (BTC): $1 (or equivalent)