In the contemporary communication landscape, sustainable social media influencers play a vital role in advocating for sustainability campaigns initiated by companies. However, audience trust in these influencers can be challenged by perceived biases. This study examines how sustainable social media influencers maintain authenticity and credibility when collaborating on sustainability campaigns. Internal and external challenges are identified, and strategies such as strong self-identity, co-creation, and consistency are employed to address them. The findings underscore the importance of transparency and ethical communication in fostering trust and driving positive social change. This research sheds light on the critical role of influencers in promoting authenticity and credibility, particularly in the context of sustainability advocacy.