Hello LeinAd,
First of all, I hope you know that the BTC_USDT.ERC20 market has Bitcoin as the base currency and Tether as the quote currency. If this is not what you want, you should swap the currencies around. The format that the plugin uses for markets is BASE_QUOTE, not QUOTE_BASE.
It is not possible to change the currency symbol. The .ERC20 part is there to distinguish this token from the USDT token on the Omni layer.
(You can however modify the name and icon using the appropriate WordPress filters. The filter for the Tether icon URL is wallets_coin_icon_url_USDT.ERC20.)
In any case, this issue arises due to CoinPayments having a USDT.png icon file, while the token symbol is USDT.ERC20. I have updated the coin adapter to remove the .* part from symbols, when it looks for icon files.
Thank you for spotting this issue. Please install the latest version 1.1.4 of the adapter to resolve the issue.
with regards
P.S. I have moved this thread to the CoinPayments forum because it turns out that it has to do with the coin adapter.