There isn't a spot that shows your ROI on the Trex wallet and any wallet for that matter. Afaik you must manually figure out what price you bought in for (either bitcoin or fiat) and then see what the value is of the coins you hold now. I have yet to see a website that neatly calculates it for you and that is because it isn't their job to do this, it is ours.
Check out
https://chainswap.io. Is that similar to the type of service that you're talking about? It's so much easier than having to manually calculate the value of a certain crypto
I allready see some profits from altcoins, but i dont know which one earned me most profit. Is it possible to just cash out the
profit and not sell all your coins?
This seems like a pretty simple thing to do if you're fairly decent at math. You can clearly see how many altcoins you exchanged, and at the price that you exchanged them for. Convert that into a dollar amount, and then do the same conversion for the coins that you're holding at current values. Subtract the original exchange price, and the difference is what you should be able to sell at a profit. It's a manual process, but the cool thing about most exchanges is that you can indicate how much of a coin you want to sell using its own value, the value of BTC, or the fiat value of whatever you're exchanging it for. Check out the multiple options when creating a sell order.
