If an explanation or story is unconvincing, it does not sound or seem true or real.

They gave some unconvincing explanations for the system failure. 关于这个系统的失灵，他们给出了一些令人难以信服的理由。

The dialogue was unconvincing, partly because it was American actors trying to speak London English. 对白听起来不真实，部分原因在于明明是美国演员，却非要说一口伦敦腔。