The developer /u/pinhead26 released a new tool that allows you to break BIP70 Bitpay invoices into legacy invoices as this invoice is not supported by all walets.

All you have to do is open your BitPay invoice and copy the payment URL and then paste it into this website: https://matthewzipkin.com/bitcointoolkit/, click on the output and it will probably open in whatever wallet you have. This is a use it at your own risk software as this ignores the ‘expiry’ of the invoice which may cause a problem in sending expired payments to merchants.

Bitpay also checks the coming transactions for sufficient miner fees so you’ll have to manually set a fee that is good enough for the transaction to confirm.

BitcoinToolkit

A discussion was started on the lightning-dev mailing list regarding a part of the LN spec which indicates that the amount is an optional field for Lightning invoices. This allows for the creation of an invoice with no amount specified for donation type of payments.

Issue #534 was opened in the c-lightning project and the feature was added with PR #545 on 2018-01-09.

Issue #564 was opened in the lnd project however at the time of this writing it has not been added to the project.