Bug(payments): `stg_enghouse__taps` has null `payment_reference` values

[mrtopsyt]

Describe the bug
As a payments data engineer, I expect the Enghouse stg_enghouse__taps table to have a non-null payment_reference value in all entries. This value is important to link individual taps entries to link to Enghouse transactions and ticket_results entries, as well as Elavon transactions entries. Currently, there are entries where this value is null, so they cannot be linked.

To Reproduce

SELECT * from cal-itp-data-infra.staging.stg_enghouse__taps where payment_reference is null limit 100

Run this query, and see a non-empty table

Expected behavior
The above table is empty, since all payment_reference values are non-null

Additional context

Enghouse/Monet+ communication required. It appears that this case is also linked to the tx_status being equal to 2. Enghouse has not provided an explanation for how to interpret this column.