how to cancel previous job in kotlin

I'm kinda stuck right now with my implementataion, when I execute my acceptAllBlood() the generateBlood() firing off instead but if I put cancel inside the combine I have an issue that I couldn't click my backpress but the acceptAllBlood() firing off, I tried already to debug it, so when calling this acceptBlood() the job of generateBlood() is still active.

here is my viewmodel:

generateBloodJob: Job? = null
markBloodJob: Job? = null

private fun generateBlood() {
    if (generateBloodJob?.isActive == true) return
    generateBloodJob = viewModelScope.launch {
        combine(donorStreamed(), bloodAvaiable()) { donor, blood ->
            val errors =
                listOf(ErrorData, FailedToGetDonor, FailedToGetBloodAvialabilit)
            when {
                donor in errors || blood in errors -> _error.postValue(true)
                else -> if (donor is ValidDonor) {
                    factory.donorTitle(donor.title.orEmpty())
                    bloodBatch(donor)
                }
            }
            return@combine when (blood) {
                is BloodData -> {
                    getBlood(blood)
                }
                else -> emptyList()
            }
        }.collect { value -> avaiableList.value = value }
    }
}

fun acceptAllBlood() {
    if (markBloodJob?.isActive == true) return
    markBloodJob = viewModelScope.launch {
        avaiableList.value.takeIf { it.isNotEmpty() }?.forEach { urlPath ->
            acceptAllBloodApi(urlPath)
            bloodAvaiable()
                .filterIsInstance<MarkedAsAccept>()
                .collect { status ->
                    if (!status.accepted) {
                        throw IllegalStateException("Can't mark donor in $urlPath")
                    }
                }
        }
    }
}

generateBlood() here is initialized inside the init of the viewmodel. acceptAllBlood() will fire when the user click donate button. but what happen is that if I click donate , generateBlood() is triggering. I added also generateBloodJob?.cancel() inside the combine but my backpress doesn't work but it fires the acceptAllBlood().