Peace be upon you. It is forbidden to lie, which means to report something that is not true. There is no difference in the prohibition between serious statements and those made in jest unless there is a clear indication that it is meant as a joke. Otherwise, there is a concern regarding its prohibition, and it is safer to avoid it. If someone speaks in jest without intending to convey a serious message, it is permissible. The responsibility of determining the context lies with the individual. Such a statement does not make one a disbeliever.
Source: [Minhaj al-Salihin, Vol. 2, Issue 38](
https://www.sistani.org/arabic/book/15/770/).
Additionally, Ayatollah Khamenei states that lying in jest is forbidden if the statement contradicts reality and the liar intends for the listener to take it seriously. However, it is permissible if the liar does not intend to say something serious or contrary to the truth, and the listener does not take it as a serious statement. The responsibility of determining the context lies with the individual. Such a statement does not make one a disbeliever.
Source: [Special Inquiry](
https://islamq2a.com/masdar/91.jpg).
May you be successful in all good.