troubleshooting postgresql ldap authentication

posgresql 12
centos 7

i am trying to configure ldap authentication.

i have the following pg_hba.conf entry (server and basedn are correct but
not shown):

hostssl all all 0.0.0.0/0 ldap
ldapserver="ldaps://xxx" ldapbasedn="yyy" ldaptls=1

when i attempt to authenticate, i see the following in pg logs:

2020-06-08 15:58:43 CDT [20235]: [1-1]
user=[unknown],db=[unknown],app=[unknown],client=zzz LOG: connection
received: host=zzz port=12378
2020-06-08 15:58:43 CDT [20235]: [2-1]
user=uuu,db=postgres,app=[unknown],client=zzz LOG: could not initialize
LDAP: Bad parameter to an ldap routine
2020-06-08 15:58:43 CDT [20235]: [3-1]
user=uuu,db=postgres,app=[unknown],client=zzz FATAL: LDAP authentication
failed for user "uuu"
2020-06-08 15:58:43 CDT [20235]: [4-1]
user=uuu,db=postgres,app=[unknown],client=zzz DETAIL: Connection matched
pg_hba.conf line 90: "hostssl all all 0.0.0.0/0
ldap ldapserver="ldaps://xxx" ldapbasedn="yyy" ldaptls=1"

does anyone know what might be causing "LDAP: Bad parameter to an ldap
routine"

ldapsearch works fine w/ the supplied ldapserver and base dn.