reliable, honest, truthful
Credible means something that is believable or capable of being believed; believable. For example, credible evidence refers to evidence that is worthy of belief or trustworthy. In the question this means that the sponsor denial or the explanation of it, is believable or trustworthy.
It comes from the Latin "credo" to believe.
Believable is most likely to be the definition of credible.
The root word in incredible is cred. The suffix is -ible.
Believable, unquestionable, undoubted, palpable...
Shakespeare did not use the word "trustworthy" but he did use the word "trusty" a lot which means the same.
Reliable.
The word "trustworthy" means "worthy of trust". Depending on the context, it could have the synonyms reliable, dependable, steadfast, or loyal.
The word "trustworthy" is an adjective.
The word "plausible" means something that is believable or credible. The suffix "-ible" in plausible comes from Latin and means "able to be."
Saying that your book report blew out the car window is a flimsy excuse.
vishvAsapAtram = trustworthy विश्वासपात्रम्