We are also thinking of using ERPNext for our company (events management) and I am under the assumption that you are referring to something like “RMO-9-2021 Annex A” (since this is commented on 2022, the actual requirements might have changed).
I am under the assumption that the proof of ownership can be defined as:
If you will build the system from scratch (ie. setting up your own servers or renting a VPC), then you could assume the ownership of that specific machine. However, I don’t know if you could also say that you “own” a VPC as it is only exist virtually (ie. no/shared hardware is technically unownable)
If you will use Frappe’s cloud service, then it might require joint affidavit. I doubt that this can be given by Frappe, as some providers I’ve asked have a hard time understanding BIR’s requirements.
If I have the time, I could ask our local BIR office then I’ll get back to this.