(1) The contractor may demand a part payment from the customer in the amount of the value of the work they have performed and which they owe under the contract. Where the work has not been performed as contractually agreed, the customer may refuse to pay a reasonable portion of the part payment. The burden of proof as to the work corresponding to what has been contractually agreed continues to be incumbent on the contractor until acceptance. Section 641 (3) applies accordingly. The work is to be documented by a list that must facilitate a rapid and reliable evaluation of the work. Sentences 1 to 5 also apply to required materials or building components that are supplied or specially prepared and made available if, at the customer’s option, ownership of the materials or building components is transferred to them or an appropriate security is provided in this regard.
(2) The security under subsection (1) sentence 6 also may be provided by means of a guarantee or other payment undertaking by a financial institution or credit insurer authorised to operate its business in the territorial extent of this Code.