Hi, Harald. 
brouwer.nl.nu is no longer delegated to ZoneEdit name servers via nl.nu:
ig +trace brouwer.nl.nu NS
; <<>> DiG 9.10.3-P4-Debian <<>> +trace brouwer.nl.nu NS
;; global options: +cmd
.                       631     IN      NS      e.root-servers.net.
.                       631     IN      NS      d.root-servers.net.
.                       631     IN      NS      l.root-servers.net.
.                       631     IN      NS      g.root-servers.net.
.                       631     IN      NS      k.root-servers.net.
.                       631     IN      NS      h.root-servers.net.
.                       631     IN      NS      m.root-servers.net.
.                       631     IN      NS      i.root-servers.net.
.                       631     IN      NS      b.root-servers.net.
.                       631     IN      NS      a.root-servers.net.
.                       631     IN      NS      j.root-servers.net.
.                       631     IN      NS      c.root-servers.net.
.                       631     IN      NS      f.root-servers.net.
.                       1075    IN      RRSIG   NS 8 0 518400 20211223050000 20211210040000 14748 . bfBBoiXr6YW/6mgOpCcE6cjkU/WqMgmxzMJ0cNZIquThRbYCyVJTO8hx jir4OBbSrFoDJ4UvhoKhHSmfsCS0WryO33nVCx+qJjfGcWLgPpANeIr4 B978BrFO4Hh1ONzen7Mc+4Hy3LJ8pzIoW0Mmdpw42+ssHKPmcIPsNToG 5p0O3TAdcesJ7SMp5OME74+rnn019YrQhEHlcuTI/MvOLKYuB51qfTC9 +dNnAzSVoRioNGEv1wLYxMpZIRKiVCFJCANI5oWaVC/mpqGsOsmb9rjz TKEhPW6ql2cqUv0gzASNP8N8Yvh5pLN1glepl3LJ3wrwnYNBh3S8t7tN 2Tr7Dw==
;; Received 525 bytes from 64.68.199.53#53(64.68.199.53) in 1 ms
nu.                     172800  IN      NS      a.ns.nu.
nu.                     172800  IN      NS      m.ns.nu.
nu.                     172800  IN      NS      d.ns.nu.
nu.                     172800  IN      NS      c.ns.nu.
nu.                     172800  IN      NS      z.ns.nu.
nu.                     172800  IN      NS      y.ns.nu.
nu.                     86400   IN      DS      41209 13 2 46159142140BBF89ECB41E202F88DA8C7D8A51B584AA5EA4A28CEAAA F9091185
nu.                     86400   IN      RRSIG   DS 8 1 86400 20211223050000 20211210040000 14748 . Szen82UJpgsq4yaG9tAkgmW+F3ET1SQLJgJX14hom1xhD4nSPMo36v/b BbmvGHICXmkxl783RE6uSNTkE9sltgoITjuGhJ5XbP7LXoh5MIie0IOV D7OPHmlfPVhdxmGEYHcSG04+nQUO41lG089g05hRZQ3FaW/TBFkSe9mr F2U42IjMdmQjhrgJVjejt5eU0mkcryXpqtScJTYsBig4gKDwUfdpocyN I9PzH3ekXDdHnxLafuMk328kiBisPgOX9PQjXPq1zVzRCj7sdppTcjp3 W2dsmPzIF6XGe1cmR/p+B3xBGxtZljlQhcR6eCYaq/1I+H983922+ptl KBpk6Q==
;; Received 740 bytes from 198.41.0.4#53(a.root-servers.net) in 33 ms
nl.nu.                  86400   IN      NS      ns1.mydyndns.org.
nl.nu.                  86400   IN      NS      ns1.worldwidedns.net.
nl.nu.                  86400   IN      NS      ns2.worldwidedns.net.
nl.nu.                  86400   IN      NS      ns3.worldwidedns.net.
nl.nu.                  86400   IN      NS      ns1171.dns.dyn.com.
nl.nu.                  7200    IN      NSEC    nl-bestel.nu. NS RRSIG NSEC
nl.nu.                  7200    IN      RRSIG   NSEC 13 2 7200 20211221073059 20211207183510 45062 nu. D12gFNMTyH947glMBdb3mf38QF9SdDCdSwJUcC32DoV2KpyGKs32vwiD w26yyP3/7RC2RWgfmG5Kw23BN6pvTQ==
;; Received 306 bytes from 194.146.106.22#53(a.ns.nu) in 166 ms
;; Received 42 bytes from 207.97.208.112#53(ns1.worldwidedns.net) in 24 ms
Please check with how this is set up via the above name servers.