What's causing this 404 error for Apple Pay in-app provisioning?

I'm working to kickstart 'add to wallet' from inside a banking app. I need help understanding why the below request (I've redacted for security before posting) is resulting in the error seen:

default 12:20:21.855401+1000 PassbookUIService Performing request:

GET https://nc-pod2-smp-device.apple.com:443/broker/v4/devices/042142AB8C43800172352079BE12E5E8241E4/issuerProvisioningCertificates?encryptionVersion=PKEncryptionSchemeECC_V2

{

"Accept-Language" = "en-AU";

Authorization = "AppleToken 000603-05-a2a1cb73-3b1f-4dd2-95d9-056191f4be70:AAAABLwIAAAAAF7Y49QRCmdzLnBiLmF1dGi9AAamTui0xlxAXI+uSPOkZe9Wd/0NASBE1a9vqUhzKZJ0NVgZEvWqzzw7+tVelzpkA+ZTiSoV8yTmBBruhxFoRBpn6LbERDrxx3umQIN+IWwymNMNnV+RAgGWwOOxkKSoBDfoP+5w91wZW6EL5hk6IKUDbUe1HkX/YLe4F+Kl2FMedFw1qI/POR9F3dbwgmgGvbsnRA4wSGBXQuoiYSo";

"X-Apple-Client-Info" = "<iPhone10,3> <iPhone OS;13.4.1;17E262> <com.apple.PassKitCore/1 (com.apple.PassbookUIService/1.0)>";

"X-Apple-Device-Region" = AU;

"X-Apple-Web-Service-Session" = "CE391534-AB5F-09792744BEA8";

"x-apple-seid" = 042142AB8C438001723520794BE12E5E8241E4;

"x-apple-soc-type" = t8015;

}

(null)

results in:

default 12:20:22.947866+1000 PassbookUIService Response:

https://nc-pod2-smp-device.apple.com:443/broker/v4/devices/042142AB8C43800172352079BE12E5E8241E4/issuerProvisioningCertificates?encryptionVersion=PKEncryptionSchemeECC_V2 404

{

"Content-Length" = 81;

"Content-Type" = "application/json";

Date = "Fri, 05 Jun 2020 02:20:22 GMT";

"Set-Cookie" = "X-SESS=ffffffff12a9564845525d5f4f58455e445a4a427902;Version=1;path=/;secure;httponly";

Vary = "accept-language";

"X-Pod" = "nc-pod2";

"X-Pod-Region" = "paymentpass.com.apple";

"x-conversation-id" = 0b55b53cb4074c509ef548cb2d944f4d;

}

{

statusCode = 404;

statusMessage = "Broker Service Response exception";

}