# Common API data types

Common API Types used within multiple API resources.

## References

#### Reference

[type definition](/search.md?urn=ctp:checkout:type:Reference).

#### ResourceIdentifier

[type definition](/search.md?urn=ctp:checkout:type:ResourceIdentifier).

#### ReferenceTypeId

[type definition](/search.md?urn=ctp:checkout:type:ReferenceTypeId).

## Representations

#### Amount

[type definition](/search.md?urn=ctp:checkout:type:Amount).

#### Region

[type definition](/search.md?urn=ctp:checkout:type:Region).

#### DateTime

A `DateTime` is a JSON string representation of UTC date & time in [ISO 8601](https://www.iso.org/iso-8601-date-and-time-format.html) format (YYYY-MM-DDThh:mm:ss.sssZ), for example:

```json
"2018-10-12T14:00:00.000Z"
```

#### CartReference

[type definition](/search.md?urn=ctp:checkout:type:CartReference).

#### OrderReference

[type definition](/search.md?urn=ctp:checkout:type:OrderReference).

#### PaymentReference

[type definition](/search.md?urn=ctp:checkout:type:PaymentReference).

#### CartResourceIdentifier

[type definition](/search.md?urn=ctp:checkout:type:CartResourceIdentifier).

#### OrderResourceIdentifier

[type definition](/search.md?urn=ctp:checkout:type:OrderResourceIdentifier).

#### PaymentResourceIdentifier

[type definition](/search.md?urn=ctp:checkout:type:PaymentResourceIdentifier).

## Localization

#### CountryCode

[type definition](/search.md?urn=ctp:checkout:type:CountryCode).

#### CurrencyCode

[type definition](/search.md?urn=ctp:checkout:type:CurrencyCode).

#### Locale

[type definition](/search.md?urn=ctp:checkout:type:Locale).

#### LocalizedString

[type definition](/search.md?urn=ctp:checkout:type:LocalizedString).

#### LocalizedUrl

[type definition](/search.md?urn=ctp:checkout:type:LocalizedUrl).

## Client logging

These objects represent information about which [API Client](/api/projects/api-clients.md) created or modified a resource. For more information, see [Client Logging](/checkout/general-concepts.md#client-logging).

#### CreatedBy

[type definition](/search.md?urn=ctp:checkout:type:CreatedBy).

#### LastModifiedBy

[type definition](/search.md?urn=ctp:checkout:type:LastModifiedBy).

## Related pages

- [Area overview page with navigation](/checkout.md)
- [Previous page: General concepts](/checkout/general-concepts.md)
- [Next page: Errors](/checkout/errors.md)
- [Search documentation and API specs](/search.md)