The word "unconvincing" means not able to make someone believe or agree with something because it lacks evidence, logic, or is not persuasive enough. Full definition
They will be found unconvincing in a court because they relate to a report requested with the imprimatur of Congress. (climateaudit.org)
In trying to equate Liam's sudden descent into penury with the plight of his country's deprived underclass, however, Boorman ends up with a film as unconvincing as Cattrall's Irish accent. (bbc.co.uk)
However, Gatti was axed after a string of unconvincing performances by the host nation and Menotti decided to go with Fillol. (goalkeepersaredifferent.com)