El Paso, Texas — To reach the U.S. border, Carla Delgado, 23, walked across Panama's treacherous Darién jungle with her husband and four small children. In Mexico, they traveled on top of a freight train known as "the beast," a perilous ride that has caused some migrants to lose limbs or fall to their death.

By any measure, the day the family entered the U.S. was much easier. They lined up alongside several dozen migrants early on a Monday morning at the main bridge connecting El Paso with Ciudad Juárez, Mexico. After a few hours of processing, health screenings and background checks, the family was released from U.S. custody with a notice to appear in immigration court, where they will have a chance to apply for asylum.

"I'm happy because thanks to God, we reached our goal, which was to get here," Delgado said after leaving the Customs and Border Protection facility at the Paso del Norte bridge. "We are safer," said her husband, Zahyr Aguirre, 27, who had entered the U.S. days earlier. He noted the family's plan was to fly to Chicago.

The family benefited from a program the Biden administration started earlier this year to discourage unlawful border crossings by allowing migrants to use a phone app to set up an appointment at international bridges, where U.S. officials determine whether they should be allowed into the country to request asylum.

The Biden administration is planning to make the process powered by the app, called CBP One, the main portal to the U.S. asylum system at the southern border, sending the message that those who fail to wait for an appointment and attempt to enter the country without permission will be swiftly turned back.

More than 60,000 asylum-seekers have secured appointments to enter the U.S. since the CBP One app became available to migrants in mid-January, according to unpublished government data. Most of those who have scheduled appointments hail from Venezuela, Haiti, Russia, Mexico, Honduras, Cuba, Chile and Brazil.

The app is one component of a revamped border strategy President Biden unveiled in January, along with the expansion of a pandemic-era rule known as Title 42 to expel those who enter the country unlawfully and a sponsor program to admit up to 30,000 migrants from Cuba, Haiti, Nicaragua and Venezuela each month. The policies have so far led to a two-year low in apprehensions of migrants in between official border crossings.

But human rights advocates have said the strategy has also fueled an intensifying humanitarian crisis in northern Mexico, where migrants have grown increasingly frustrated by their inability to secure one of several hundred coveted appointments distributed by the U.S. each morning.

The plight of those stuck in Mexico was tragically illustrated by a fire inside a Mexican immigration detention facility in Ciudad Juárez last month that killed more than three dozen migrants. The Mexican government has maintained that a protesting migrant started the fire, though it has also arrested several guards to face charges of homicide and causing injuries.

"The future"

While advocates for asylum-seekers have called CBP One a glitchy app that has failed to provide enough spots to help the large number of desperate migrants seeking U.S. sanctuary, Republicans have denounced it as a "concierge service" for those who lack proper documents to enter the country.

Despite these concerns, Biden administration officials have defended the CBP One process as an attempt to maintain some access to the overwhelmed U.S. asylum system, while also preventing unlawful border crossings from returning to the unprecedented levels reported last year.

In fact, CBP One will continue to play a major role in the administration's border policy after May 11, when the expiration of the national COVID-19 public health emergency is set to trigger Title 42's end. 

The administration is planning to increase the number of migrants allowed to enter the U.S. daily under the CBP One process from 740 to 1,000, senior U.S. officials told CBS News, requesting anonymity to discuss internal plans. The number of participating bridges will also increase, the officials said. 

Currently, CBP One allows migrants to request humanitarian exemptions to Title 42. But after the pandemic-era rule is lifted, the app will allow migrants to avoid being subjected to a soon-to-be-published regulation that will bar migrants from asylum if they failed to seek refuge in a third country en route to the U.S. Those who fail to use the app and cross into the U.S. illegally will risk being promptly deported.

Angela Kelley, who served as a top immigration official at DHS until May 2022, said the administration is trying to "figure out what's the secret sauce of enough legal pathways and opportunities to apply for asylum so that people wait and try to cross legally, rather than with a smuggler."

"Yes, it's imperfect but it's a heck of a lot better than anything else we've had in the past. There seems to be an investment in this being the future," Kelley said.

In an interview with "60 Minutes," DHS Secretary Alejandro Mayorkas said he would not call CBP One "flawless." But he stressed the app is part of a broader effort to create a "safe and orderly" way for migrants to request U.S. asylum. Under the proposed asylum restriction, Mayorkas added, migrants won't have to use CBP One if they prove they have an urgent medical condition or are fleeing imminent danger.

"It is very much a work in progress. But we are seeing at the same time an extraordinary movement of people. The challenge cannot be overstated," Mayorkas said.

"Reducing asylum to Ticketmaster"

Anyone with a smartphone can download CBP One. But migrants seeking an exemption to Title 42 can only secure an appointment if they are north of Mexico City, due to a geofencing limit placed by U.S. officials.

The app, which is available in English, Spanish and Haitian creole, asks migrants to create a profile and submit a photo of their face and basic information, such as their legal name, nationality and date of birth.

On paper, the app says Title 42 exemptions are only available to those with a physical or mental illness or a disability; pregnant women; migrants lacking safe and stable housing in Mexico; those under the age of 21 or over the age of 70; or asylum-seekers who have been threatened or harmed in Mexico. The app, however, does not require migrants to prove they are part of one of the vulnerable groups.

Every morning at 11 a.m. ET / 9 a.m. MT, the U.S. distributes several hundred new CBP One appointments, 13 days in advance. In a matter of minutes, they're all gone. 

Blaine Bookey, the legal director of the Center for Gender and Refugee Studies at the University of California in San Francisco, called CBP One "extremely arbitrary," saying it fails to prioritize the cases of migrants with the most urgent cases, such as those victimized in Mexico or who have been waiting there the longest.

"There's no rhyme or reason to who is getting the appointments," Bookey said. "It's like reducing asylum to Ticketmaster."

Citing interviews with migrants in Tijuana, Bookey said the process, in some ways, excludes the most vulnerable of asylum-seekers, such as those who are illiterate or can't afford a phone, while giving preferential treatment to those with the best quality smartphones and access to a strong internet connection.

In a statement, the Department of Homeland Security said it had made several updates to improve CBP One, including to make it easier for parents and children to get appointments as a group. It noted that CBP was aware of delays when new spots are distributed in the morning due to increased traffic, but said the problems could also stem from "hardware issues from the end user or internet access and reliability."

"CBP is not seeing any discernible difference or indication that any particular group is being disadvantaged based on the number of applications," the department said.   

The app did not help Guadalupe Vásquez de Jesús, 32, and her three children enter the U.S. A widowed mother from an indigenous community in southern Mexico, Vásquez de Jesús said she fled north after her husband was killed and her youngest son hit by a stray bullet. Her son, she added, needed medical attention to remove bullet fragments from his left eye, but had not been able to get care in Mexico.

In February, Vásquez de Jesús traveled to the Paso del Norte bridge to implore U.S. officials to let her family in, but they were denied entry, prompting her to break down in tears during an interview with Telemundo. She waited at a shelter in Ciudad Juárez for two months, each day trying to get an appointment — to no avail.

"I don't know what to do. My other son, the one who had the accident, just wants to go home. But I don't want to go back. I'm not going back," Vásquez de Jesús said in an interview with "60 Minutes" last month.

Vásquez de Jesús' fortunes changed only after lawyers intervened and told U.S. officials the family had an urgent humanitarian case. On April 4, less than two days after she was featured on "60 Minutes," Vásquez de Jesús and her three children, Rene, 9, Ricardo, 7, and Aleida, 3, returned to the bridge near El Paso.

Initially, U.S. officers told her she could not enter without a CBP One appointment. But the advocates traveling with Vásquez de Jesús said the family had been approved to enter the U.S. outside of the CBP One program. The family's plight had also been covered by "60 Minutes," the officers were told.

After a second group of officers arrived, Vásquez de Jesús and her children were allowed to enter the U.S. With Ricardo leading the way, the family took their first steps on American soil on the same bridge where they had been rejected just weeks earlier.

Andy Court and Annabelle Hanflig contributed reporting.

Camilo Montoya-Galvez

Camilo Montoya-Galvez is the immigration reporter at CBS News. Based in Washington, he covers immigration policy and politics.

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