Is it possible to create a Bill Payment that is not linked to a Bill yet? Then, link afterwards once it's traced.

That sounds like a vendor prepayment. The handy thing about vendor prepayments is that you can link it to a PO. Then when the Bill is created from the PO, NS will auto apply the prepayment to the bills that was associated with that PO.

Actually, no. It's a Bill Payment. The bill came first. We just can't trace it yet.

just take it as a payment

This is for Vendors.

no, you can't create a vendor payment that isn't associated to a vendor bill.

It looks like a Vendor Prepayment transaction without nominating a PO. Let’s call it Vendor “pre-applied“. It’s then available to apply to the required Bill.