People hoping to send checks to a fundraiser to build President Donald Trump’s border wall will have to send their money to a Castle Rock UPS store where unnamed “business associates” of the original GoFundMe creator will retrieve the mail.

The online fundraiser started by Florida motivational speaker Brian Kolfage on Sunday has generated international headlines and more than $9 million in three days for the president’s project, which has become the crux of an impending government shutdown.

Trump said Thursday he would not sign a budget bill that would keep the government operational after Friday if it did not include money for the wall. The president has previously said he would be “proud” to shut down the government for the wall.

People hoping to contribute to the online fundraiser can donate online or send a check to the UPS store, next to a Baskin Robbins in a strip mall at 4833 Front St. in Castle Rock, according to the fundraising page. The page applauds Trump and says Americans should “pitch in” to get the border wall started.

One fraud expert said the postal box was odd but, in general, GoFundMe is reputable. The Colorado Secretary of State’s Office, which regulates nonprofits doing business in the state, said it did not have authority over the fundraiser.

“I don’t even know what kind of legal enforcement anyone would be able to have over that,” said Julia Sunny, spokeswoman for the Colorado Secretary of State’s Office.

Kolfage first said in an email to The Denver Post that he is using the Castle Rock address because he has business partners near there who are helping him manage the fundraising campaign until he gets more volunteers.

In a later email, Kolfage declined to name those business partners and said they had “nothing to do with any of this, they are just helping me with mail.” He said it was difficult for him to go to a post office box every day because he is a triple amputee.

Kolfage was seriously injured during a rocket attack in Iraq while working in the U.S. Air Force in 2004, according to his website. He lost his legs and his right arm as a result. The veteran now lives in Miramar Beach, Fla., where he works as a motivational speaker and previously served on former Arizona U.S. Rep. Gabrielle Giffords’ veterans advisory council.

Kolfage did not respond to a question about how the checks will be sent to him but said he would refund the money if the GoFundMe does not reach its $1 billion goal. Kolfage updated his fundraising page Thursday to say all checks should be made out to “GoFund The Wall” but did not respond to an email asking whether that was a bank account or an organization created to receive donations. Previously, the page did not list whom the check should be made out to.

Kolfage said he had not received any donations via check as of Thursday afternoon.

Employees at the UPS store in Castle Rock had not heard of the fundraiser until a Denver Post reporter called. Franchise owner Todd Hunter said he could not disclose who rents the mailboxes at the location.

“This is the first we’ve heard of it,” Hunter said.

An investigations coordinator with the Better Business Bureau of Greater Denver and Central Colorado didn’t know what to say after the situation was explained to him.

“That’s really strange,” Ezra Coopersmith said.

The GoFundMe has a lot of unanswered questions, Coopersmith said, but Kolfage acknowledges the uncertainties up front.

“To this guy’s credit, he lays those all out,” he said. “I don’t see that many issues that would make me question the integrity of the campaign.”

However, having anonymous people pick up checks in a town across the country from the founder is unusual, Coopersmith said.

“Sending a check to a mailbox that is owned by someone you don’t know doesn’t scream transparency,” he said.

Instead, he recommended people donate through the online page and noted that GoFundMe is generally a safe way to contribute to fundraisers.

GoFundMe did not respond to questions sent via email for this story, but its website notes that people running fundraisers can add donations made outside the website to a cause’s goal.

Kolfage is not the first person to solicit individual contributions for a border wall. Arizona state legislators voted in 2011 to create a fundraising website for the project. The state raised only $265,000 of its $50 million goal, however. Other individuals have also launched their own online fundraisers, but most failed to raise more than a few thousand dollars.

It’s unclear whether the government could use the money for such a project.

Two Republican U.S. representatives have filed bills to allow the U.S. Department of the Treasury to accept public donations for the wall. Both bills are in committee.

The Department of the Treasury states on its website that people can donate to the federal government for general use. However, those gifts are considered unconditional.

Kolfage said he has talked with the Trump administration but declined to elaborate to The Washington Post.

The Washington Post and The Associated Press contributed to this report.