Hello,
With a free plan, you get 1000 requests per month on fixer. If you have rates set to update every hour, this is 24*30 or 720 requests per month. Additionally the plugin performs a request every time you activate the plugin and whenever you click the exchange rates refresh button. So it is not unlikely for you to approach the limit near the end of the month. As today is the 29th of April, the limit will be reset in two days from now.
I will investigate the issue with CoinMarketCap, but please open a new thread for each issue in the future. I believe that some of the currencies you have enabled such as USDT.E may have a different symbol/ID on CoinMarketCap. If so, this is something that I will be able to fix in the next release of the plugin. Thank you for reporting this. I will keep you updated.
with regards