Use kotlinx.coroutines.delay(...) inside a coroutine instead of Thread.sleep(...).

Thread.sleep blocks the current thread. delay suspends the coroutine without blocking the thread, so other coroutines can keep running.

import kotlinx.coroutines.delay
import kotlinx.coroutines.runBlocking

fun main() = runBlocking {
    println("Before delay")

    delay(1_000) // suspends for 1 second, does not block the thread

    println("After delay")
}

If you currently have:

Thread.sleep(1000)

replace it with:

delay(1000)

But note: delay is a suspend function, so it can only be called from another suspend function or from inside a coroutine builder such as launch, async, or runBlocking.

Example with launch:

import kotlinx.coroutines.delay
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking

fun main() = runBlocking {
    launch {
        delay(1000)
        println("Coroutine finished after 1 second")
    }

    println("This prints immediately")
}

Example in a suspend function:

import kotlinx.coroutines.delay

suspend fun doWork() {
    delay(500)
    println("Work done")
}

Avoid doing this in coroutines:

Thread.sleep(1000) // blocks the underlying thread

Prefer:

delay(1000) // suspends only the coroutine