I have few questions

1) how can i attach an invoice to a customer Service Request (SR)?
2) Which custom API should i use for this purpose?
3) Once the status for service request changes to “Closed”, we change disputed amount on the corresponding invoice to zero,How do i go about it?
4) how can the concept of hooks be used in this case?

any pointers to this will be really helpful.

Thanks & Regards
Nishant