cant save my Bitpay (bitcoin) address to the Bitpay / WooCommerce plugin

Check this:
https://www.ads-software.com/extend/plugins/bitcoin-payments-for-woocommerce/

Plugin that allows you to accept bitcoins at your store without paying fees to anyone.

If your payment gateway for WooCommerce does not store the settings you enter, please make sure the gateway has been made compatible with WooCommerce 2.0. Your issue sounds exactly like the one you should be having when the gateway has not been updated yet, so please ask your plugin developer to update the code (if there is not yet an update available).