[Investigate] Discrepancy between line item amounts and invoice amounts

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Describe the issue

In our internal Stripe data, we've noticed that not all amounts in the line item table tie up to the amounts in the invoice table, when summed up to the invoice grain. So far it's been identified that it ties to a subscription amount found in the price_plan table.

We should confirm whether this is something buggy with our data, or if this is indeed expected and we should make adjustments in our logic.

### Relevant error log or model output

_No response_

### Expected behavior

Invoice line item amounts sum up to the amounts in the invoice table

### dbt Project configurations

na

### Package versions

na

### What database are you using dbt with?

other (mention it in "Additional Context")

### dbt Version

na

### Additional Context

_No response_

### Are you willing to open a PR to help address this issue?

- [X] Yes.
- [ ] Yes, but I will need assistance and will schedule time during our [office hours](https://calendly.com/fivetran-solutions-team/fivetran-solutions-team-office-hours) for guidance
- [ ] No.

Start by comparing the line item and invoice tables at invoice grain, then trace the subscription amount in the price_plan table. Confirm whether the discrepancy is expected Stripe data behavior or a data-modeling bug, and document or implement the required logic adjustment.

Written by the indexing model from the issue text.