Someone's credentials are their previous achievements, training, and general background, which indicate that they are qualified to do something.
her credentials as a Bach specialist.
她作为一名巴赫研究专家的资历。
Someone's credentials are a letter or certificate that proves their identity or qualifications.
The new ambassador to Lebanon has presented his credentials to the president.
驻黎巴嫩新任大使已经向总统呈递了国书。