Why am I unable to swap 2 tokens?

Is the "swap" button grayed out next to some tokens?

All available pairs are listed in the fee policy, under the "Calculation of exchange fees per pair" section. Your tokens are not listed?

Then you will have to withdraw them either on:

Steps to follow are detailled in the answer to the question "How to withdraw the cryptocurrencies in my Meria portfolio to an external wallet?"