In an exchange, there are two countries.
The data is incomplete. You mention only one country instead of two and their populations.
The error message is saying exactly what the problem is.
you cannot exchange workers is there are not enough to exchange.
or one of the two is exchanging more than 400.000
Please first check is there are sufficient numbers.
if there are, then give me the names of BOTH countries.
and the numbers you try to exchange if these numbers are indeed available.
A country with less than 35.000.000 cannot send anyone to any other country.