Recommended approach for data conversion of customer account contacts users for iReceivables

Hello Folks

I am wondering if there is any support note or documentation of the recommended approach for an initial data conversion of many customer account contacts/users in order to allow them use iReceivables.

I have read

Conversion of Customers in R12 Receivables

thread which does not address iReceivables additional necessary details (external user, roles, customer data access)

and found

How Can An External User Be Automatically Created In iReceivables?(Doc ID 2367983.1)

which suggests to use Self Registration process.

However my current customer implementation is looking for any method to automate this process using APIs.

Thanks