Sysctl settings for transmission bittorrent (udp receive buffer size)

I can't get transmission (bittorrent client) to work properly.

From the logs:
transmission-daemon: UDP Failed to set receive buffer:
requested 4194304, got 41600

On Linux I would do:
sysctl net.core.rmem_max=4194304
I couldn't figure out the correct settings for OpenBSD.

net.inet.udp.recvspace sets the default, not the max buffer size,
e.g. sysctl net.inet.udp.recvspace=4194304 causes errors:
nslookup openbsd.org
nslookup: isc_socket_create: not enough free resources

My system:
OpenBSD 7.1 (GENERIC) #438: Tue Apr 5 10:30:52 MDT 2022
transmission-3.00p0

Any ideas? Best wishes,
Daniel.