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I also started using the Cryptomus instant trading platform instead of the conversion feature to exchange BTC to USDT, in fact this is much better because you can set the price you choose to sell instead of the instant conversion price which is not in line with the market price most of the time.
The problem as you mentioned is that there are only a few pairs, in addition to that I wrote in a previous post about the problems I encountered regarding the lack of the page refresh feature and writing the price manually, but unfortunately these problems have not been solved yet, I hope the development team will notice all these problems and work on solving them in the near future.
When I tried to transfer USDT using the Solana network, a notification appeared that I couldn't use it (I haven't had time to capture the screenshot). I don't know whether there was a problem with the Solana network or the Cryptomus wallet because there were no problems when using the Solana network in several previous transactions. So, I switch to using the BSC network (BEP-20) for the transactions.
So far, there have been no problems with the convert, spot trading, or transfer features using Cryptomus, except for issues with one of the USDT networks I mentioned above.