Site-to-Site VPN Issues

I am testing a new XGS 136 (SFOS 20.0.0 GA-Build222) offsite to replace an onsite XG 135 (SFOS 19.0.2 MR-2-Build472). The backup of the XG 135 was used to setup the XGS 136.

We have never used the IPsec Site-to-Site connection before but may have a use for it further down the line. Therefore, before I put the new unit into production I thought I would take the opportunity to test the Site-to-Site feature. However, I cannot initiate the connection. Here are the settings that I have (note that the local and remote ID are the same email address on both ends).

Head Office Settings on XG 135

Branch Office Settings

I can successfully activate both ends of the connection.

However, when I try to connect on either end, I get the following error.

I checked /log/strongswan.log on the branch end and got the following "KE payload missing in message" and UNSUPPORTED_CRITICAL_PAYLOAD errors:

2024-04-10 07:55:02Z 06[CFG] vici initiate 'Test-1'
2024-04-10 07:55:02Z 15[IKE] <Test-1|55> ### queue_child invoking quick_mode_create
2024-04-10 07:55:02Z 15[IKE] <Test-1|55> ### quick_mode_create: 0x7fe3a4002650 config 0x7fe3bc0038c0
2024-04-10 07:55:02Z 15[IKE] <Test-1|55> initiating Main Mode IKE_SA Test-1[55] to HEAD_OFFICE_IP_ADDRESS
2024-04-10 07:55:02Z 15[ENC] <Test-1|55> generating ID_PROT request 0 [ SA V V V V V V ]
2024-04-10 07:55:02Z 15[NET] <Test-1|55> sending packet: from BRANCH_IP_ADDRESS[500] to HEAD_OFFICE_IP_ADDRESS[500] (548 bytes)
2024-04-10 07:55:02Z 17[NET] <56> received packet: from BRANCH_IP_ADDRESS[500] to HEAD_OFFICE_IP_ADDRESS[500] (548 bytes)
2024-04-10 07:55:02Z 17[ENC] <56> parsed ID_PROT request 0 [ SA V V V V V V ]
2024-04-10 07:55:02Z 17[IKE] <56> received XAuth vendor ID
2024-04-10 07:55:02Z 17[IKE] <56> received DPD vendor ID
2024-04-10 07:55:02Z 17[IKE] <56> received Cisco Unity vendor ID
2024-04-10 07:55:02Z 17[IKE] <56> received FRAGMENTATION vendor ID
2024-04-10 07:55:02Z 17[IKE] <56> received NAT-T (RFC 3947) vendor ID
2024-04-10 07:55:02Z 17[IKE] <56> received draft-ietf-ipsec-nat-t-ike-02\n vendor ID
2024-04-10 07:55:02Z 17[IKE] <56> BRANCH_IP_ADDRESS is initiating a Main Mode IKE_SA
2024-04-10 07:55:02Z 17[ENC] <56> generating ID_PROT response 0 [ SA V V V V V ]
2024-04-10 07:55:02Z 17[NET] <56> sending packet: from HEAD_OFFICE_IP_ADDRESS[500] to BRANCH_IP_ADDRESS[500] (180 bytes)
2024-04-10 07:55:02Z 16[NET] <56> received packet: from HEAD_OFFICE_IP_ADDRESS[500] to BRANCH_IP_ADDRESS[500] (180 bytes)
2024-04-10 07:55:02Z 16[ENC] <56> parsed ID_PROT request 0 [ SA V V V V V ]
2024-04-10 07:55:02Z 16[IKE] <56> received XAuth vendor ID
2024-04-10 07:55:02Z 16[IKE] <56> received DPD vendor ID
2024-04-10 07:55:02Z 16[IKE] <56> received Cisco Unity vendor ID
2024-04-10 07:55:02Z 16[IKE] <56> received FRAGMENTATION vendor ID
2024-04-10 07:55:02Z 16[IKE] <56> received NAT-T (RFC 3947) vendor ID
2024-04-10 07:55:02Z 16[IKE] <56> KE payload missing in message
2024-04-10 07:55:02Z 16[ENC] <56> generating INFORMATIONAL_V1 request 102214803 [ N(CRIT) ]
2024-04-10 07:55:02Z 16[NET] <56> sending packet: from BRANCH_IP_ADDRESS[500] to HEAD_OFFICE_IP_ADDRESS[500] (56 bytes)
2024-04-10 07:55:02Z 27[NET] <Test-1|55> received packet: from BRANCH_IP_ADDRESS[500] to HEAD_OFFICE_IP_ADDRESS[500] (56 bytes)
2024-04-10 07:55:02Z 27[ENC] <Test-1|55> parsed INFORMATIONAL_V1 request 102214803 [ N(CRIT) ]
2024-04-10 07:55:02Z 27[IKE] <Test-1|55> informational: received UNSUPPORTED_CRITICAL_PAYLOAD error notify
2024-04-10 07:55:02Z 27[IKE] <Test-1|55> ### destroy: 0x7fe3a4002650

Can anyone spot any obvious issues?