javax.ws.rs.ProcessingException: reactor.netty.ReactorNetty$InternalNettyException: io.netty.util.internal.OutOfDirectMemoryError: failed to allocate

Question

I am seeing reactor.netty.ReactorNetty$InternalNettyException: io.netty.util.internal.OutOfDirectMemoryError: failed to allocate 16777216 byte(s) of direct memory (used: 1056964615, max: 1073741824) issue while calling an external client B from my application A.

I had following questions:

a) Interestingly, this happens only for a certain external client call, my application is a large scale real time app making multiple downstream/external client calls but none of them fails. Is there any correlation?

b)Why the external client call needs a direct memory access? Is it a default behavior for all external client calls or upon some configuration?

c) If latter is the case, how one can decide the apt size for direct memory?

Thanks for your response.