NMM_Exchange.php non-USD conversion issues

[rmwb]

FYI
The free currency conversion API used in NMM_Exchange.php to convert non-USD totals back to USD for further conversion to crypto values, is currently offline/down. https://www.currencyconverterapi.com/server-status
There's backup code that uses fixer.io, but it is also offline/returning an error, because the hardcoded API key has reached its monthly usage limit.
"Your monthly usage limit has been reached. Please upgrade your Subscription Plan."

The result seems to be a zero total for all orders in all cryptocurrencies right now, assuming your WooCommerce currency setting is anything other than 'United States (US) Dollar'.

Also, the fixer.io code seems to have a logic error. It looks like it falsely assumes the results will be returned with a USD base rate, but the actual base rate on the free tier of fixer.io is EUR.
https://fixer.io/documentation#basecurrency