How the Flexfield code AR_PAYMENT_SCHEDULES works

Summary:

I've a business requirement to add a flexfield for Transaction Installments.

This flexfield need to be read/populated using any API/Webservice.

Content (required):

I've created a segment under flexfield code AR_PAYMENT_SCHEDULES but I don't know how to work with this (how to read/insert information under attribute1).

I know about the REST endpoint receivablesInvoiceInstallmentGDF, but this one only works with Installment regional information, and I'm not able to add new fields there.

Version (include the version you are using, if applicable):

23B

Code Snippet (add any code snippets that support your topic, if applicable):

Regards,

Wilson