SQL Server 2019

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

DECLARE @CONTACTS varchar(max)
SET @CONTACTS = 
N'[
{"contacts":"[{\"idRole\":1,\"cdsid\":\"RWILS351\"},{\"idRole\":3,\"cdsid\":\"EKANOUS\"},{\"idRole\":126,\"cdsid\":\"RLAESCH1\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"RWILS351\"},{\"idRole\":3,\"cdsid\":\"EKANOUS\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"OINES\"},{\"idRole\":1,\"cdsid\":\"YSEGARRA\"},{\"idRole\":3,\"cdsid\":\"OINES\"},{\"idRole\":3,\"cdsid\":\"TISMAIL3\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DBELL30\"},{\"idRole\":3,\"cdsid\":\"DBELL30\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DBELL30\"},{\"idRole\":3,\"cdsid\":\"DBELL30\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2},{\"pmtGroup\":5}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2},{\"pmtGroup\":5}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":1,\"cdsid\":\"DSANGINE\"},{\"idRole\":3,\"cdsid\":\"DSANGINE\",\"idAttribute\":[{\"pmtGroup\":2}]},{\"idRole\":3,\"cdsid\":\"EDESMET\"},{\"idRole\":126,\"cdsid\":\"NSPENC16\"}]"},
{"contacts":"[{\"idRole\":3,\"cdsid\":\"THERMANN\"}]"}]'

SELECT d.idRole, d.cdsid,e.pmtGroup
FROM  OPENJSON (@CONTACTS)
WITH (
    contacts nvarchar(max)
) as c 
CROSS APPLY OPENJSON (c.contacts) 
WITH (
    idRole INT,
    cdsid NVARCHAR(50),
    idAttribute NVARCHAR(MAX) AS JSON
) as d
OUTER APPLY OPENJSON(d.idAttribute)
WITH (
    pmtGroup NVARCHAR(8)
) as e;

SELECT d.idRole, d.cdsid,d.pmtGroup
FROM  OPENJSON (@CONTACTS)
WITH (
    contacts nvarchar(max)
) as c 
CROSS APPLY OPENJSON (c.contacts) 
WITH (
    idRole INT,
    cdsid NVARCHAR(50),
    pmtGroup NVARCHAR(8) '$.idAttribute[0].pmtGroup'
) as d;

idRole	cdsid	pmtGroup
1	RWILS351	null
3	EKANOUS	null
126	RLAESCH1	null
1	RWILS351	null
3	EKANOUS	null
1	OINES	null
1	YSEGARRA	null
3	OINES	null
3	TISMAIL3	null
1	DBELL30	null
3	DBELL30	null
1	DBELL30	null
3	DBELL30	null
1	DSANGINE	null
3	DSANGINE	2
3	DSANGINE	5
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	DSANGINE	5
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
3	THERMANN	null

idRole	cdsid	pmtGroup
1	RWILS351	null
3	EKANOUS	null
126	RLAESCH1	null
1	RWILS351	null
3	EKANOUS	null
1	OINES	null
1	YSEGARRA	null
3	OINES	null
3	TISMAIL3	null
1	DBELL30	null
3	DBELL30	null
1	DBELL30	null
3	DBELL30	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
1	DSANGINE	null
3	DSANGINE	2
3	EDESMET	null
126	NSPENC16	null
3	THERMANN	null