a document specific to Serbian laws, not requested anywhere else where holding a promissory note is more than enough, the promissory note being being by definition "irrevocable" and in itself more than enough proof of the right to demand payment;

a sample: [http://www.euroturs.rs/aranzmani/2012/12/03-menicno-ovlascen...]

[http://www.aktivasistem.com/upload/documents/387f9c-Menica k...]

the most usual term is to "cash a promissory note" i.e. demand cash in exchange for the "promissory note" (as promised by the note)

more rarely used: "to realise" a promissory note:

DIGEST OF CASES. - HeinOnline
heinonlinebackup.com/hol-cgi-bin/get_pdf.cgi?handle=hein...39‎
a trustee in insolvency is entitled to realise a promissory note which the insolvent has pledged to a creditor. T, the holder of a promissory note, pledged the note ...
[http://heinonline.org/HOL/LandingPage?handle=hein.journals/s...]

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Note added at 1 day1 hr (2014-04-04 22:53:00 GMT)
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Asking for an additional "irrevocable letter of authorisation to cash/realise the promissory note" seems like rather redundant even when compared to the definition of what is a bill of exchange/a promissory note in Serbia:

Menica - Pismeni dokument, izdat u strogo zakonskoj formi, u kome se izdavalac (trasant) obavezuje da će u roku isplatiti određeni iznos, ili pak poziva drugo lice (trasata) da izvrši tu isplatu. Postoji više vrsta menica.
Jedna od njih je sopstvena - kada se izdavalac obavezuje da će sam izvršiti isplatu, dok je vučena ona kojom izvršilac poziva drugo lice, odnosno trasata da izvrši isplatu.
Blanko menica je neispunjen menični obrazac snabdeven potrebnim potpisima i zakonski može postati menica čim se ispune ostali bitni podaci. Blanko menica se upotrebljava za obezbeđenje zajma pojedinca ili organizacije - ako dužnik normalno otplaćuje zajam, pri izvršenoj potpunoj uplati blanko menica se vraća dužnicima. Ali ako dužnik prestane sa otplatama blanko menica se popunjava na ostatak duga, a dug se isplaćuje po meničnom postupku. Sve izjave u vezi sa menicom daju se napismeno i potpisano na menici, a svaki potpisnik na menici je i obaveznik.
[http://www.kamatica.com/pojam/menica]


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Note added at 2 days10 hrs (2014-04-06 07:28:57 GMT)
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and also compared with the standard definition of a promissory note:
"Definition of 'Promissory Note'

A financial instrument that contains a written promise by one party to pay another party a definite sum of money either on demand or at a specified future date. A promissory note typically contains all the terms pertaining to the indebtedness by the issuer or maker to the note's payee, such as the amount, interest rate, maturity date, date and place of issuance, and issuer's signature. The 1930 international convention that governs promissory notes and bills of exchange also stipulates that the term “promissory note” should be inserted in the body of the instrument and should contain an unconditional promise to pay.

Investopedia explains 'Promissory Note'

Promissory notes lie somewhere between the informality of an IOU and the rigidity of a loan contract in terms of their legal enforceability. An IOU merely acknowledges that a debt exists, but does not include a specific promise to pay, as is the case with a promissory note. A loan contract, on the other hand, usually states the lender’s right to recourse – such as foreclosure – in the event of default by the borrower; such provisions are generally absent in a promissory note.

Promissory notes that are unconditional [neopozive] and saleable [prenosive] become negotiable instruments that are extensively used in business transactions in numerous countries.

A promissory note is usually held by the payee. Once the debt has been discharged, it must be cancelled by the payee and returned to the issuer."