Can a text message resignation be regarded as a written signed resignation application?

I work in human resources, and the resignation message via text message cannot be used as a formal resignation application. A written form is required, and the most convenient is a written resignation letter or resignation application.

Reference: "Labor Contract Law"

Article 37 The employee may terminate the labor contract by notifying the employer in writing 30 days in advance. During the probation period, the employee can terminate the labor contract by notifying the employer three days in advance.