The issue here is to make them believe that your income is from the crypto trading! You need some documented proof to establish the fact that you have not made such income by selling illegal things.
Every exchange you work with, must have something called "trading history" which can be downloaded from the exchange website itself. It can be a PDF or an Excel file that provides the details of your trades executed within a certain range of dates. Keep such documents handy so that it can be produced when required. It is also needed during your tax filings.
Also keep your last years tax document handy if you haven't hidden any information. That should suffice to counter the questions and arguments of the ignorant immigration officers. Hope this helps!