Certify the month against the mediciones

Record what is executed against each partida for the period as a percentage of its contract quantity. The earned quantity follows from that percentage and the design quantity, and the earned amount from the same percentage and the position total, so one honest number per line produces the whole valuation.

Why: A certificacion built from a single project percentage cannot be checked and therefore cannot be approved without a conversation. Measured line by line, the disagreement is about one partida rather than about the whole month, and the rest of the money moves while that one is settled.

Read the valuation back against the bill, capitulo by capitulo, and check the rates it used are the contract rates. Where a partida has been measured past the quantity the contract carries, deal with it as a change to the position with an order behind it rather than as a larger figure on the same line.

Why: An exceso certified quietly is an exceso the property can refuse at the final account, months after the work was built and paid for down the chain. Raising it as a change while it is small is the only version of that conversation where you are not asking to be paid for work already done.

Route the certificacion to the direccion facultativa, and on a public contract to whoever the contract adds after them. Keep the approval date, because the invoice follows the approval and the payment clock in the next step runs from the invoice, so an approval that slips moves everything behind it.

Why: Approval sitting in an inbox is the most common reason a certificacion is late, and it is invisible while it is happening because nobody has refused anything. A route with a date on each hop turns that into a question with an owner instead of a monthly complaint.

Raise the invoice against the approved certificacion, carrying the retention and any deduction the contract provides for, and reference the certificacion number on it. Where the work is between businesses the VAT treatment may be inversion del sujeto pasivo rather than a rate.

Why: An invoice for a figure nobody approved is an invoice that will be returned, and the clock does not start on a returned invoice. Matching it to the certificacion also means the accounts and the valuation tell the same story at year end without anybody reconciling them by hand.

Put the invoice on the payment clock under the European late-payment regime, which is what Ley 3/2004 implements in Spain. Thirty days between businesses by default, extendable to sixty by express agreement and no further unless the term is not grossly unfair, with interest at the European Central Bank reference rate plus eight points from the day it is missed. There is no Spanish regime of its own in the register, so on a public contract read the periods the LCSP fixes against the date it gives you.

Why: Late payment is normal in this market and interest is almost never claimed, which is precisely why it keeps happening. A tracked due date does not require you to claim anything; it just means the conversation happens on day thirty-five rather than at the final account, when nobody remembers which month was late.