Is it permissible to give Zakat al-Mal (obligatory charity) to someone who advertises their need online or begs in the street, given the difficulty of verifying their truthfulness?

Zakat should only be given after careful investigation and knowledge, or a strong presumption, that the recipient is eligible. If the zakat payer gives zakat while doubting that the recipient is one of its rightful beneficiaries, and has not investigated, or has investigated but it did not become clear that the person is eligible, then the payment is invalid, unless it later becomes clear that they are eligible. Some scholars are of the view that if it is difficult to ascertain whether a beggar who asks people is eligible for zakat or not, they should first be informed that this is zakat and that it is not permissible for them to take it if they are not eligible. Then, it can be given to them if they state that they are eligible.