error: pool6 refused acquire: bad preferred prefix! (1)

I get the error

pool6 refused acquire: bad preferred prefix! (1)

when providing a/56 prefix to a UNIFI UXG using dhcpv with the following configuration:

> /ipv6/pool/print 
Flags: D - DYNAMIC
Columns: NAME, PREFIX, PREFIX-LENGTH, EXPIRES-AFTER
#   NAME      PREFIX                    PREFIX-LENGTH  EXPIRES-AFTER
1   office    2001:db8:110b:fe00            56    

> /ipv6/dhcp-server/export  
# jan/13/2023 18:33:52 by RouterOS 7.6
# software id = BR1Z-L1D0
#
# model = CCR2004-1G-12S+2XS
# serial number = D4F00C670F4A
/ipv6 dhcp-server
add address-pool=office interface=sfp-sfpplus4 name=office rapid-commit=no

> /ipv6/address/export 
# jan/13/2023 18:34:56 by RouterOS 7.6
# software id = BR1Z-L1D0
#
# model = CCR2004-1G-12S+2XS
# serial number =...
/ipv6 address
add address= 2001:db8:110b:101::1 advertise=no interface=sfp-sfpplus4

On ubnt size I’m only setting dhcpv6 to get a /56 prefix.

Any idea what could be the issue?

I get the same error

Then you made the same mistake…

The pool is 2001:db8:110b:fe00::/56 not only 2001:db8:110b:fe00