API Monitoring: Checking uptime vs checking if your response actually works

Lately, API monitoring has been on my mind. The majority of tools (such as Pingdom and UptimeRobot) only verify that your API is returning a 200 OK.

However, what if the response structure has changed but your API is returning 200 OK? similar to:

Prior to:

{
    "user": {
        "name": "John"
    }
}

Following:

{
    "user": {
        "full_name": "John"
    }
}

Monitoring reports are ok and the API returns 200, but your frontend is broken.

1. Are you on the lookout for this? How?
2. Has "breaking changes with 200 OK" ever caused you any pain?
3. What equipment do you use? What irritates you?

Currently, it appears that the following options are available: Postman Monitors ($49/user/month; too expensive)
Checkly (nice but complicated)
Create your own scripts.

Interested in the opinions of the community? Is this actually a problem?