Did you really have configured your slapd with dynamic runtime configuration as described in the
Wiki?
You may verify by
ldapsearch -Y EXTERNAL -H ldapi:/// -b "cn=schema,cn=config" dn
SASL/EXTERNAL authentication started
SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
# extended LDIF
#
# LDAPv3
# base <cn=schema,cn=config> with scope subtree
# filter: (objectclass=*)
# requesting: dn
#
# schema, config
dn: cn=schema,cn=config
# {0}core, schema, config
dn: cn={0}core,cn=schema,cn=config
# {1}cosine, schema, config
dn: cn={1}cosine,cn=schema,cn=config
# {2}nis, schema, config
dn: cn={2}nis,cn=schema,cn=config
# {3}inetorgperson, schema, config
dn: cn={3}inetorgperson,cn=schema,cn=config
# {4}dicom, schema, config
dn: cn={4}dicom,cn=schema,cn=config
# {5}dcm4che, schema, config
dn: cn={5}dcm4che,cn=schema,cn=config
# {6}dcm4chee-archive, schema, config
dn: cn={6}dcm4chee-archive,cn=schema,cn=config
# {7}dcm4chee-archive-ui, schema, config
dn: cn={7}dcm4chee-archive-ui,cn=schema,cn=config
# search result
search: 2
result: 0 Success
# numResponses: 10
# numEntries: 9
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