Hi Jerome,
Thanks for your quick response. After several attempts, I finally managed to resolve this issue. The devil is in the details... The mistake was the beneficiary used: it should have been "Interactive Brokers LLC, etc." and not myself.
Another interesting element: I transferred 1500$ from my swissquote account to my IB account. Swissquote charges 10.- for each withdrawal, nothing new. When transferring, I clearly specified "All fees to be paid by the beneficiary (BEN)". However, I received 1465$ on my IB account instead of 1500$ - this means that there are fees of 25$ that I cannot explain at the moment. I also made a transfer of 1000.- CHF from my zac account to IB and in this case, I ended up with 1000.- CHF on the IB account. Note: this time, I was not asked about the fees (paid by the sender or the recipient).