Following is copied from v1.1 IG:
Payment details. Generally can be structured or unstructured information but banks have possibilities to
set different rules according their own additional services. Please contact your bank regarding remittance
information. Usage Rule: When the client fills both, the structured and unstructured information tags, but the bank cannot forward both tags, then creditor reference under the structured information will be lifted to the unstructured information tag in accordance with EACT standard for unstructured remittance information formatting rules. If the remittance information as a result will be longer than 140 characters, then the bank will deliver only 140 characters of the remittance information. For example /RFB/XXXXXX/TXT/ZZZZZZ, where RFB stands for the code of creditor reference, XXXXXX stands for the creditor reference, TXT stands for the code of unstructured information and ZZZZZZ stands for the unstructured information.
Unstructured payment details. More information about EACT standard for unstructured remittance information
can be found in the following page: http://www.eact.eu/main.php?page=SEPA
Structured payment details. Used for entering reference number required by beneficiary.