custom property not being set using node.js SDK

payload like so: 
 

const subscribe: SubscriptionCreateJobCreateQuery = {
      data: {
        type: ProfileSubscriptionBulkCreateJobEnum.ProfileSubscriptionBulkCreateJob,
        attributes: {
          profiles: {
            data: a
              {
                type: ProfileEnum.Profile,
                attributes: {
                  email: toEmail,
                  subscriptions: {
                    email: {
                      marketing: {
                        consent: "SUBSCRIBED",
                      },
                    },
                  },
                  properties: {
                    submissionId,
                  },
                },
              },
            ],
          },
        },
        relationships: {
          list: { data: { type: "list", id: listId } },
        },
      },
    };
    const response = await profilesApi.subscribeProfiles(subscribe);

properties: { submissionId }

This value is not present in the UI when I submit the profile - I can the contact has been created in the UI, but the proeprty is not being set. 

Am I doing something wrong? 

Thanks.