Up until the S8, you could get an extension kit where you can put in two sim cards and the microSD card into the hybrid slot, it meant your second sim card was hanging outside the phone however and for mine, it was between the phone and the case and it meant when I traveled to another country, I could easily swap the second sim without needing to access the tray. They have since programed the phones to stop this from being allowed now which is a shame.
The alternative was to physically remove the chip from the microSD and combine it with the second sim so that they both sat in the phone together, this however meant chopping up your microSD for this purpose. Whilst this worked in a similar way to the above, this is also no longer allowed.
When trying either methods now, you just get a message saying there is something unidentified in the sim tray.
So do I, however when the phone detects two sims AND a memory card all at the same time, it will throw up an error message saying to check the sim card tray rendering it useless until you remove either a sim card or memory card.