BIG-IP Next HA Pair Onboarding REST API

I've been playing around with BIG-IP Next in my home lab for the past few days and have managed to successfully onboard an HA pair of BIG-IP Next instances via the BIG-IP Next Central Manager GUI.

I am now trying to do the same thing, but this time with the REST API. However, when I attempt to do this, I receive the following error when checking the onboarding task from Postman :

"failure_reason": "failed to save details about new onboarding node (address 10.1.0.242)",

I am using the following JSON documented under the 'Deploy an Onboarding Manifest' heading (I have just substituted the property values to reflect my lab environment) and I am sending the API call to the Central Manager management IP.

https://clouddocs.f5.com/products/big-iq/mgmt-api/v0.0.1/ApiReferences/bigip_public_api_ref/r_openapi-next.html#operation/DeployOnboardingManifest

Out of interest, has anyone managed to get this working?