S2D not joining Echo Plus ZigBee coordinator

Question

I'm beginning to prototype a Zigbee router/end-device using the S2Ds from my ZigBee Mesh Kit. I'm trying to use an Amazon Echo Plus as a coordinator. To start, I'm following the examples of others who managed to get S2C Xbees talking to SmartThings hubs :

https://nzfalco.jimdo.com/electronic-projects/xbee-to-smartthings/
https://forums.parallax.com/discussion/157233/propeller-to-smartthings-communicating-with-the-zigbee-ha-public-profile

I've also found a post from someone who was able to get an S2C to join an Echo+ coordinated PAN :

https://forums.developer.amazon.com/questions/110325/xbee-and-echo-plus-communication.html

I'm using the usual HA ZigBee settings on the S2D for a router:

ID 0
CE 0
ZS 2
AP 1
AO 3
EE 1
EO 2
KY 0x5A6967426565416C6C69616E63653039

I put the Echo+ into discovery mode and issue a reset to the S2D, but it never finds a PAN. I've tried playing with some of the other firmware options but nothing seems to allow me to join. Has anyone had any luck with an Echo+ coordinator? Or am I maybe missing a crucial setting on the S2D?

Thanks, Kristian

Comments

I've dug a bit further by enabling verbose join.  It appears I am seeing beacons from the coordinator, but these are immediately followed by "Reject ZS" status frames.  Here's an example of what I'm seeing:

Extended Modem Status (API 1)

7E 00 11 98 04 FF B4 9B D2 0B 01 3D 13 44 83 0D 11 40 80 02 40

Start delimiter: 7E
Length: 00 11 (17)
Frame type: 98 (Extended Modem Status)
Status: 04 (Beacon Response)
Status Data: FF B4 9B D2 0B 01 3D 13 44 83 0D 11 40 80 02
Checksum: 40



Extended Modem Status (API 1)

7E 00 02 98 05 62

Start delimiter: 7E
Length: 00 02 (2)
Frame type: 98 (Extended Modem Status)
Status: 05 (Reject ZS)
Checksum: 62


I believe the beacon frame indicates that the Echo+ coordinator is open to join and supports ZS=2.  I have ZS=2 set on the S2D.  If I've understood correctly, it's the S2D that is rejecting the beacon, although I'm unsure as to why.  Might anyone have an idea?

Thanks, Kristian