Is earning profit from an application that relies on watching or interacting with videos, or on investing the application's currency to increase its value, permissible or forbidden, and is investing the currency within the application considered usury?

Watching videos and viewing images for digital currency is permissible, provided the content is free from forbidden elements and the compensation (ju'al) is known. This transaction is considered a ju'alah (commission-based contract), which stipulates that the ju'al must be specified. As for unknown tickets and gifts granted by the application, they render the transaction invalid.

Regarding inviting others to receive a diamond box, there is no harm in it if the contents of the box are known and it does not involve paying subscription fees, in order to avoid prohibited multi-level marketing.

Furthermore, giving the application 4000 units to receive 6000 after a week constitutes riba (usury) of both types (nasi'ah - delay, and tafadul - excess) because it involves exchanging money for money with delay and an increase.

In summary, dealing with the application is permissible if the compensation is known and it can be used without falling into forbidden acts. However, if the compensation is unknown, or if its use is only possible by committing a forbidden act, then it is not permissible to deal with it.