What if a WhatsApp Message is Used as an Admission of Guilt?

Imagine a murder case where the prime accused sends a WhatsApp message to a friend, saying, "Main kar diya," which translates to "I've done it." The message is sent hours after the crime took place and is saved on the friend's phone. In this scenario, can the prosecution use this WhatsApp message as an admission of guilt under Section 30 of the Indian Evidence Act, 1872, which deals with admissions against interest?

Considering the BSA (Bombay Shops and Establishments Act) doesn't directly apply here, we'd focus on the Indian Evidence Act. If the WhatsApp message is admitted as evidence, does it automatically become admissible as a confession made by the accused? What are the potential caveats and limitations in using this message as evidence?