The fields needed depend on the source and the reconciliation objective. The following examples support the scoping discussion; they do not imply that every source contains every field.
A booking reference or ticket number, travel dates and service type help establish the travel context. The available booking version and any changes also matter.
A transaction or invoice reference, amount, currency and relevant dates describe the billing side. Charges and credits need to remain distinguishable.
The company entity, traveller reference and, where available, a cost centre or project code provide additional context. Availability and permitted use are agreed with the parties involved.
The connected data should make a match verifiable, not merely produce a record that looks similar.