1412020-10-22 04:43:13Oct 22 04:43:13PBS_DrayTek## IKEv2 DBG : Recv IKEv2_SA_INIT[34] Reply from 78.32.***.***, Peer is IKEv2 Responder
1412020-10-22 04:43:13Oct 22 04:43:13PBS_DrayTek## IKEv2 DBG : Received IKEv2 Notify IKEv2_INVALID_SYNTAX[7]
1412020-10-22 04:43:13Oct 22 04:43:13PBS_DrayTek## IKEv2 DBG : Missing payload : IKEv2_NP_v2SA+0x82
1412020-10-22 04:43:13Oct 22 04:43:13PBS_DrayTek## IKEv2 DBG : Process Packet : Parse payload failed
1412020-10-22 04:43:16Oct 22 04:43:16PBS_DrayTek## IKEv2 DBG : Recv IKEv2_SA_INIT[34] Reply from 78.32.***.***, Peer is IKEv2 Responder
1412020-10-22 04:43:16Oct 22 04:43:16PBS_DrayTek## IKEv2 DBG : Received IKEv2 Notify IKEv2_INVALID_SYNTAX[7]
1412020-10-22 04:43:16Oct 22 04:43:16PBS_DrayTek## IKEv2 DBG : Missing payload : IKEv2_NP_v2SA+0x82
1412020-10-22 04:43:16Oct 22 04:43:16PBS_DrayTek## IKEv2 DBG : Process Packet : Parse payload failed
1412020-10-22 04:43:22Oct 22 04:43:22PBS_DrayTek## IKEv2 DBG : Recv IKEv2_SA_INIT[34] Reply from 78.32.***.***, Peer is IKEv2 Responder
1412020-10-22 04:43:22Oct 22 04:43:22PBS_DrayTek## IKEv2 DBG : Received IKEv2 Notify IKEv2_INVALID_SYNTAX[7]
1412020-10-22 04:43:22Oct 22 04:43:22PBS_DrayTek## IKEv2 DBG : Missing payload : IKEv2_NP_v2SA+0x82
1412020-10-22 04:43:22Oct 22 04:43:22PBS_DrayTek## IKEv2 DBG : Process Packet : Parse payload failed
1412020-10-22 04:43:25Oct 22 04:43:26PBS_DrayTek[IPSEC][L2L][1:Stafford_C][@78.32.***.***] IKE link timeout: state linking
1412020-10-22 04:43:30Oct 22 04:43:30PBS_DrayTekDialing Node1 (Stafford_C) : 78.32.***.***
1412020-10-22 04:43:30Oct 22 04:43:30PBS_DrayTek## IKEv2 DBG : IKESA outI1 : Create IKE SA #6512 Profile Index 0
1412020-10-22 04:43:30Oct 22 04:43:30PBS_DrayTek## IKEv2 DBG : Recv IKEv2_SA_INIT[34] Reply from 78.32.***.***, Peer is IKEv2 Responder
1412020-10-22 04:43:30Oct 22 04:43:30PBS_DrayTek## IKEv2 DBG : Received IKEv2 Notify IKEv2_INVALID_SYNTAX[7]
1412020-10-22 04:43:30Oct 22 04:43:30PBS_DrayTek## IKEv2 DBG : Missing payload : IKEv2_NP_v2SA+0x82
1412020-10-22 04:43:30Oct 22 04:43:30PBS_DrayTek## IKEv2 DBG : Process Packet : Parse payload failed
1412020-10-22 04:43:33Oct 22 04:43:33PBS_DrayTek## IKEv2 DBG : Recv IKEv2_SA_INIT[34] Reply from 78.32.***.***, Peer is IKEv2 Responder
1412020-10-22 04:43:33Oct 22 04:43:33PBS_DrayTek## IKEv2 DBG : Received IKEv2 Notify IKEv2_INVALID_SYNTAX[7]

(Back to IKE V1) - I don't suppose selecting "Auto" for 'IKE phase 1 proposal' works?

I can't help but feel, that the officially retired 3DES is the root cause of this - there are a few configuration examples around for SonicWall <-> Draytek, but they all use AES.

It's past my bedtime now - good luck with it!

A very helpful lady at Sonicwall support managed to sort it out for me - also she was happy to work on the Draytek too.
I will post the config when I have some time.

@hornbyp - many thanks for your help and input - especially in the wee small hours!

Simon.

I'll be interested to hear how you got it working...

https://www.cru-technologies.co.uk/wp-content/uploads/2020/10/Site%20to%20Site%20Sonicwall%20to%20Draytek.pdf
Draytek 5 - TCP/IP network settings - Local Network IP (of 10.0.0.0) was used rather than the network specific IP of 10.1.3.0.
And the same on the Sonicwall for the VPN Network Object (10.0.0.0 was used).
Once I had these settings, I have successfully setup an additional two Draytek - SW VPN's.
Hope this helps someone!

Simon.