JOHN YANG: The U.S. Customs and Border Protection says that in July, arrests of people illegally crossing the U.S.-Mexico border were the lowest they've been in nearly four years.

It comes after the Biden administration imposed new rules intended to encourage migrants to use legal pathways to seek asylum.

There's even an app for that.

But as Gustavo Solis of KPBS in San Diego reports, the app isn't always helping the most vulnerable migrants.

JOE BIDEN, U.S. President: Migrants will be restricted from receiving asylum at our southern border unless they seek it after entering through an established lawful process.

GUSTAVO SOLIS (voice-over): When President Joe Biden announced the new restrictions in June, he said asylum seekers should use existing legal pathways to enter the United States.

JOE BIDEN: Those who seek come to United States legally, for example, by making an appointment and coming to a port of entry, asylum will still be available.

GUSTAVO SOLIS (voice-over): Make an appointment.

Sounds easy, and it is, at least in theory, all you have to do is download the CBP One on your smartphone, fill out the application and schedule an appointment.

But in practice.

JEREMY JONG: The app is famously glitchy.

In preparing for this interview, I tried to use the app.

I downloaded the app and I tried to make an appointment, and it glitched out.

GUSTAVO SOLIS (voice-over): That is Jeremy Young.

He's an attorney with Al Otro Lado, a nonprofit law firm that represents migrants with asylum claims.

And Young says that CBP One has bigger problems than just being glitchy.

JEREMY JONG: Not everyone has a smartphone.

GUSTAVO SOLIS (voice-over): Migrants without smartphones cannot get appointments.

Also the app only comes in three languages, so good luck if you do not speak English, Spanish or Haitian Creole.

And using the app is practically impossible for migrants with certain disabilities, for example, people who are blind.

JEREMY JONH: What the app does effectively is it precludes these people from the asylum process.

GUSTAVO SOLIS (voice-over): The app's biggest problem might be that demand heavily outweighs supply.

There are only 1,450 CBP One appointments available every day, but tens of thousands of migrants trying to get one.

JEREMY JONG: What you're doing is you're funneling everyone into one line, and the line is already longer than any line you've ever seen in your life.

GUSTAVO SOLIS: President Biden's executive actions do not increase the number of CBP One appointments.

Already, the average wait time in Tijuana is seven months, and local officials worry that shelters will overflow with people waiting for appointments.

Jasmine an asylum seeker from Mexico, says that the long wait times are taking a toll on everyone's mental health.

JASMINE, Mexican Asylum Seeker (through translator): There's a lot of anxiety and depression here in the shelters, especially among the women and children.

GUSTAVO SOLIS (voice-over): She says that a lot of the women and children in the shelter are depressed and anxious.

Some of the women are experiencing hair loss.

JASMINE (through translator): Yes, it's frustrating.

Several mothers here are going bald.

The ones who have waited here five or six months.

GUSTAVO SOLIS: Mariam, a woman traveling with her two teenage sons, started to cry when asked her how long she had been waiting.

WOMAN (through translator): It's been such a long time to wait.

We're fleeing because of organized crime back home.

GUSTAVO SOLIS (voice-over): Maria says she decided to flee her home in the Mexican state of Michoacan after a local drug cartel burned her business to the ground and tried to recruit her sons.

She doesn't feel safe in Tijuana.

Maria has tried to request asylum in person at the legal border crossing, but every time, border patrol agents just keep turning her back telling her to use the CBP One app.

MARIA, Mexican Asylum Seeker (through translator): They say that we have to cross legally.

But what do we do if there are no legal options available?

GUSTAVO SOLIS (voice-over): Maria says she wants to follow the legal process, but she's starting to lose hope, and she's not alone.

Officials in Tijuana say CBP One's long wait times actually contribute to illegal crossings.

Enrique Lucero is head of Tijuana's Migrant Affairs Department.

He says roughly 1/3 of migrants who cross the border illegally only do so after they try to schedule CBP One appointments.

ENRIQUE LUCERO, Migrant Affairs Officer, Tijuana, Mexico (through translator): They come in with a lot of post-traumatic stress.

They want to come across as quickly as possible, because they believe that whatever they're fleeing will follow them to Tijuana.

GUSTAVO SOLIS (voice-over): He says migrants lose hope after waiting several months.

Lucero believes that forcing more migrants to use the app without increasing the number of appointments could intensify the crisis that Biden says he's trying to solve.

ENRIQUE LUCERO (through translator): If you're going to impose these new rules, then you should increase the number of CBP One appointments, right?

GUSTAVO SOLIS (voice-over): In June, several immigrant advocacy groups filed a lawsuit to block the new rules.

For PBS News Weekend, I'm Gustavo Solis in Tijuana.