Intermittent issue when assigning a bank account to a supplier site with SOAP API PayerDetailService

This is implemented in an OIC flow that creates the bank account then assigns to a customer site.

Intermittently the bank account is not assigned at the site level but to the customer account. This issue occurs intermittently, sometimes it works other times it doesn't. Assignment to the account level seems to be because the AccountSiteUseId is not being included in the create process as shown below.

We're performing processPayerBankAccount for SOAP API PayerDetailService.

Mapping fields as follows…

On run…

Inspecting Message sent…

Inspecting Message received… Note: AccountSiteUseId now has no value

Inspecting Message processed…

Can anyone provide pointers as to why this is happening? Should we be providing the ExternalPayerId in the mapping?