The student's excuse was unconvincing. As much as she tried to make her story sound true, it was an unconvincing tale.
A lot of the evidence against Joe Bloggs was unconvincing, so the jury acquitted him.
Unconvincing means seeming false.
The antonym of convincing is unconvincing, which means not able to persuade or influence someone effectively, lacking the power to sway opinions or beliefs.
unconvincing
A character may come across as unconvincing if their actions or dialogue seem inconsistent with their established traits or background, if they lack depth and complexity, or if they are not realistically motivated in the story. Unconvincing characters may also lack relatability or fail to evoke genuine emotion from the audience.
The opposite of "convincing" is "unconvincing." While convincing refers to something that effectively persuades or influences belief, unconvincing denotes a lack of persuasive power or credibility. It describes arguments, evidence, or presentations that fail to inspire trust or acceptance.
unconvincing and confrontational
having dimensions of height and width only. In a literary sense, shallow, superficial and unconvincing characters
This may be the verb or noun "inconvenience" (a disruption or hardship).The word most closely related to convince is "unconvincing" (not plausible).
Quote from Gilbert and Sullivan (The Mikado)"gives an air of verisimilitude to an otherwise bald and unconvincing argument". I always used to say at work "If you want to convince someone of your facts - have them typed. Typing gives any case an air of verisimilitude" PS and it is spelled verisimilitude with 4 i's
unbelievable, incredible, beyond belief,inconceivable, unthinkable, unimaginable; unconvincing, far-fetched, dubious,implausible, improbable, unrealistic; hard to swallow.
Joss Whedon