http://privexqvhkwdsdnjofrsm7reaixclmzpbpveefiu4uctfm2l4mycnwad.onion
The system will detect
this and offer to allow you to "finalize" the underpayment to add a lower USD amount to your invoice. This means you can mix and match different cryptocurrencies when paying your invoice, e.g. pay $50 in Bitcoin,
pay $20 in STEEM, and pay $10 in EOS.