Messages from quack

Quack is a service that sends SMS messages with verification codes. The examples of the SMS messages show different numerical codes and all contain similar wording, indicating they are sent for account verification purposes. However, it's not clear which specific app or website uses Quack to send these verifications as no further information was provided in either the web search results or the text message content itself. Additionally, there were several definitions found online related to quacks being fraudulent medical practitioners; however this does not seem relevant to understanding what kind of service "Quack" provides based on its use case within the received texts themselves.