ExternalPurpose1Code
ExternalPurpose1Code is used for defining the purpose of the payment. For example defining payment type to be salary with pain.001.001.03 credit transfer initiation message it is done this way:
<Purp>
<Cd>SALA</Cd>
</Purp>
External code lists are defined in ISO20022 standard. The full list of codes can be found from ISO20022 pages at http://www.iso20022.org/external_code_list.page