Return to port

My RTP message is rejected for the reason; The Return to Port Declaration has been rejected as it has an activity date / time exceeding more than 1 hour in the future.

It is not allowed to send your return to port message more than 1 hour ahead of the current time. You can send your return to the port when you are entering the port.

How do I keep (a part of) the catch onboard?

The manual for keeping fish onboard can be found here

My RTP message is rejected for the reason: You have submitted an RTP declaration for a logbook C2125020200005 that has already had an RTP declaration only LAN and TRA allowed.

You already send an RTP message to the government, only a landing declaration or transport message is allowed to be sent.