# How PSI Works
source: https://developer.mastercard.com/open-finance-us/documentation/products/pay/psi-tools/how-psi-works/index.md
Note: This documentation has been updated to describe the latest PSI endpoints which add support for an unauthorized return score. For details of the legacy endpoints, see [Legacy PSI Endpoints](https://developer.mastercard.com/open-finance-us/documentation/products/pay/psi-tools/legacy/index.md).
PSI offers two regulatory API versions: an [FCRA](https://www.ftc.gov/legal-library/browse/statutes/fair-credit-reporting-act)-compliant version and a non-FCRA version.
Both versions use the same models and return the following:
* **Non-sufficient funds (NSF) score** -- Risk of insufficient funds (R01)
* Ranging from 0-100, forecasted up to 10 days to predict optimal payment timing
* **Unauthorized return score** -- Risk of unauthorized return (R10)
* Ranging from 0-100 for the current day
## Choosing a Version {#choosing-a-version}
The FCRA version is required when rejecting transactions using the NSF score, while the Non-FCRA version can be used when timing transactions based on the NSF return days. Both versions support transaction rejection based on the unauthorized return score.
[FCRA Version](https://developer.mastercard.com/open-finance-us/documentation/products/pay/psi-tools/psi-fcra/index.md) -- Use when evaluating transactions based on
non-sufficient funds score \& unauthorized return score.
* Requires that the [customer record](https://developer.mastercard.com/open-finance-us/documentation/access-and-config/customers/index.md) has an email address
* Requires you to provide an [FCRA permissible purpose code](https://developer.mastercard.com/open-finance-us/documentation/products/lend/permissible-purpose-codes/index.md) in the API request
* Includes a consumer dispute process (via the [Finicity portal](https://developer.mastercard.com/open-finance-us/documentation/products/pay/psi-tools/psi-fcra/index.md#fcra-requirements-by-participant))
* FCRA-compliant
[Non-FCRA Version](https://developer.mastercard.com/open-finance-us/documentation/products/pay/psi-tools/psi/index.md) -- Use when evaluating transactions based only on
the unauthorized return score.
* Customer email address is optional
* No dispute process required
* Ideal for fraud mitigation without triggering FCRA compliance obligations
Both versions use the same non-sufficient funds \& unauthorized
return models for the API response.
## Output Insights {#output-insights}
## Interpreting the Scores {#interpreting-the-scores}
Each of the two risk scenarios is scored on a scale from 0 to 100,
where **higher scores indicate lower risk**.
Tip: Think of it like a school exam -- a higher score is better.
* A score of 100 means that the transaction is highly likely to succeed or that the payment is very likely to be legitimate.
* A score of 5, on the other hand, suggests the transaction is less likely to succeed, either due to non-sufficient funds or potential unauthorized returns.
For example:
* A **non-sufficient funds score of 5** means the account is unlikely to have enough funds to cover the transaction.
* An **unauthorized return score of 5** could mean that the transaction was initiated by a third-party fraudster, or in some cases, by the actual account holder engaging in known first-party fraud.
| Risk Score Value | Meaning |
|------------------|------------------------------------------------------------------------------------------------------|
| 0-10 | **High Risk** - the account has a high risk of insufficient funds or unauthorized fraud return |
| 11-30 | **Medium Risk** - the account has a moderate risk of insufficient funds or unauthorized fraud return |
| 31-100 | **Low Risk** - the account has a low risk of insufficient funds or unauthorized fraud return |
Tip: You will receive NSF risk scores for the current day and up to 10 days in the future. Consider settling on the day with the highest NSF score (lowest risk), while factoring in the unauthorized return score. Note: The score interpretation provided here is for general guidance only. Actual performance may vary based on your specific transaction data and risk tolerance. The PSI team can assist in performing this analysis and sharing tailored threshold recommendations.
## Interpreting the Optional Reason Codes {#interpreting-the-optional-reason-codes}
Reason codes help explain what's driving the non-sufficient funds
`compositeScore` value (this feature is currently only available for the NSF scores).
You can think of reason codes as impact scores showing which factors had the most
influence.
There are 8 possible reason codes:
| **Reason Code** | **Description** |
|-------------------|----------------------------------------------------|
| recentBalance | Balance trends over a recent time period |
| balanceHistory | Balance trends over a complete time period |
| nsfHistory | Returns over a complete time period |
| recentNsfHistory | Returns over a recent time period |
| recurringNsf | Pattern of repeat behavior for NSF |
| spendHistory | Spend trends over a complete time period |
| depositHistory | Deposit trends over a complete time period |
| transactionAmount | Amount relative to a typical spend for the account |
* Higher reason code values (e.g. 81-100) mean those reasons had a **strong impact** on the overall score.
* These reasons can be **positive or negative** --- meaning that they could either increase or decrease the risk scores.
| Reason Code Value | Meaning |
|-------------------|--------------------------------------------------------------------------------------|
| 0-50 | **Low Influence** - the reason code has low to no influence on the composite score |
| 51-80 | **Medium Influence** - the reason code has moderate influence on the composite score |
| 81-100 | **High Influence** - the reason code has high influence on the composite score |
Examples:
