Gold Coast Mayor Tom Tate's troublesome trip to US President Donald Trump's holiday retreat at Mar-a-Lago has thrown up another twist, after a key invoice could not be found within council.

The mayor's office has explained the absence by saying the feisty politician only brought a paper invoice about the Florida trip into the office once, then took it away with him and no-one took another copy.

The invoice is an important part in how Mr Tate had nullified conflict of interest concerns about a proposed $1.5 billion Trump Tower on Gold Coast beaches earlier this year.

He had faced an outcry after initially declaring having received free accommodation at Mar-a-Lago from the Trump Organization, while the controversial tower was proposed within council boundaries.

But Mr Tate later changed his declaration to say he had personally paid for accommodation during his three-day trip in February at the exclusive club based on 20 acres of landscaped gardens alongside the Atlantic Ocean.

The politician maintained he had always intended to pay himself but an invoice "was not received promptly".

"When I asked for the invoice on check out, they didn't have it," he said in September.

"I followed it up, I got the invoice, and we got it paid."

The four-term mayor has declined to hand over the invoice and now proclaimed the trip — for which he was invited as mayor and for which ratepayers paid airfares — was "private".

Council has twice rejected ABC right to information requests for the invoice. In an internal appeal, a council officer explained no copy was found in any council systems, emails or physical records.

"The office of the mayor further advised that the mayor brought a physical copy into the office, retained it with him when he left, and that it was not printed, copied, saved or otherwise managed by the office of the mayor staff," they wrote.

They indicated they would not demand it either: "I do not believe [council] has a present legal right or practical ability to require production of that privately held copy."

Transparency International Australia chief executive Clancy Moore said that ideally some record of the invoice should be recorded for record-keeping purposes.

"Otherwise, it could be perceived as the old 'the dog ate my homework' excuse," he said.

"There is clearly a lot to explain about this trip, the nature of the hospitality, the costs, and the extent that the mayor was there on official, private or personal business."

Outstanding questions include about how much the mayor was charged. He has declined to say the amount but insisted he did not get "mate's rates".

His office issued a single line in response to questions: "The office of the mayor has fulfilled all (right to information) requirements."

Other private information about the February trip has been released previously: Council has detailed how Mr Tate spent more than $13,000 personally upgrading flights.

The whole trip proved controversial after the mayor initially boasted of dining with the president at Mar-a-Lago, describing an evening of tomahawk steaks and expensive wine at the club, founded by Mr Trump in 1995.

But the ABC later revealed a sparsity of documentation and that the White House said the president "did not have dinner" with the mayor. The Trump Organization further branded Mr Tate's account as a "complete fabrication", saying the president only briefly said hello to the mayor's table from the patio.

Mr Tate at a press conference maintained: "Recollections may vary."

During questioning at that conference about the trip accounts and his payments, a frustrated Mr Tate eventually told a journalist to "f—k off", twice, and stormed out.

The Gold Coast mayor had also said he was invited to Mar-a-Lago by the Trump Organization, and not the Queensland developer working with the organisation for the proposed $1.5 billion tower.

No record of the invitation turned up in right to information requests. The mayor's office said that was because the "invitation was issued verbally".

The Trump Tower proposal, which had attracted almost 100,000 objection petitioners, eventually collapsed.