In the study, the effectiveness of four reminder messages was evaluated through an online laboratory experiment involving 2,963 participants. The content of these messages was designed based on evidence from behavioural sciences, and their effect was contrasted with that of a simple, brief, and direct message (control message). The impact of the reminders was measured through four outcome variables: the action participants declared they would take after receiving the message, understanding and clarity of the content, and confidence in the received message. The experiment concluded that the most effective message is the one labelled “Full Payment (T2),” which, in addition to reminding of the payment due date, encourages the payment of the total billed amount by informing that it is the only way to avoid additional interest charges.