incorrect work with specific symbol names

[mytarmail]

I have a futures account and these are the names of the trading symbols

@ES , @M2K , @EU6 . . . . .

when i call MT5.Marketwatch() i get two vectors

MT5.Marketwatch()
[1] "c(\"CLE\", \"DB\", \"DSX\", \"ENQ\", \"EP\", \"EU6\", \"GCE\", \"GLE\", \"MES\", \"RTY\", \"DD\")"
[2] "c(\"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"\", \"EURUSD\")" 

when i try to get get mt5R::MT5.BidAskBook(sSymbol = "@EU6") i get error Error in if (server_resp == "") return(NULL) : argument is of length zero

how to fix it ?