Q: Is it legal for app developers to ban a user on the basis of a rule that isn’t written anywhere in the terms of use?

A: In the United States, app developers generally have broad discretion to manage their platforms and user accounts, including the right to ban users. However, their actions should be consistent with their own terms of use or service agreements. If the terms do not explicitly prohibit having more than one account and this was used as the reason for the ban, there could be grounds to challenge the action, particularly if the terms were not easily accessible or clear.

However, challenging an app developer's decision can be complicated. Most terms of service agreements include clauses that give the developers wide latitude in managing user accounts and content, often without needing to provide a detailed reason for bans or account suspensions. Additionally, private companies are generally not required to provide the same level of due process as government entities.

If your friend wishes to pursue this, he might consider escalating the issue through the app's internal complaint or appeal process, if available. Alternatively, he could voice his concerns publicly, such as through social media or app review platforms, which sometimes prompts companies to address the issue. However, legal action can be costly and time-consuming, and the success is uncertain given the broad powers typically granted to app developers in their user agreements.

It's always advisable to carefully read and understand the terms of service of any platform to avoid such situations. If you feel strongly about this issue, consulting with an attorney to explore potential legal avenues based on the specific details of the case could be the next step.