How to fix response CEA - failed Result-Code AVP: 5012?

To work with the diameter protocol, I use the library https://github.com/fiorix/go-diameter.
When I try to send CER (Capabilities-Exchange-Request) to the diameter-server, I get a failed Result-Code AVP: 5012.
I think these are unspecified reasons. I don't have access to the server logs.
How to solve this error on the client side ?
Where do I start with the diagnostics?

Im not familiar with this library, however you can find all result-codes here: result-codes

5012 means:

DIAMETER_UNABLE_TO_COMPLY 5012 This error is returned when a request is rejected for unspecified reasons.

There are 2 options to your situation:

1. There is some problem with your CER, so the Diameter node you are trying to reach is sending you back CEA with result-code 5012.
2. The open source library you are trying to use do not let you send the CER and gives you a message with 5012 as a response to your CER.

To solve the issue:

1. If your CER went to the network take a capture using wireshark/tcpdump and make sure you received CEA. You can look at your CER and check what is wrong with it (you can also send it here). Maybe your CER is not according to RFC 3588/6733?
2. If the library do not let you send the CER look at the library log and see if you can spot any error. If you do see an error you can consult the guy who wrote the library.