Which informal fallacy is committed in the statement: 'Famous singer Mr. Shantanu says ABC toothpaste boosts our immunity, therefore we must buy ABC toothpaste'?

The argument rests on a famous singer endorsing a medical benefit, which is an appeal to inappropriate authority.

A citation of authority supports a claim only when the authority is an expert in the relevant field.

A singer has no expertise in immunity or medicine, so his word lends no rational weight to the health claim.

The move from the singer saying so to we must buy it therefore has no logical force.

Trusting an authority outside its proper domain names this fallacy.