Possible bad battery, possible bad converter/charger. You'll need to do some troubleshooting to determine if the converter/charger is working properly.
You can follow the troubleshooting guide in the WFCO Owner's Manual.
I would guess your trailer is a 50 amp shore power model? If so, then your power center is a WF9500 series. I'd guess a WF9560 with a 60 watt converter/charger.
You can download the owner's manual here:
https://wfcoelectronics.com/product/wf-9560/
Pages 9 and 10 are the troubleshooting procedures and "logic tree".
MAKE SURE TO COMPLETELY DISCONNECT THE BATTERY WHEN TROUBLESHOOTING... If you leave the battery connected, you can't determine if the converter voltage readings are correct or if you're reading the battery voltage, so the battery must be completely disconnected from the system before troubleshooting.
Once you download the manual and look it over, if you have any questions, just ask. It's a fairly straightforward procedure, but can get confusing if you're not sure of what you're doing.
NOTE: If your trailer has a 30 amp shore power system, then the power center is a WFCO 8955 and the converter/charger is a 55 amp unit. The Owner's Manual is located here:
https://wfcoelectronics.com/product/wf-8955e/ and the troubleshooting guides are on pages 8-9.