The good option here is to monetize your app users’ data - you can capitalize on users without zero extra efforts. The best thing here is that its 100% GDPR compliant as you deal only with non-personal data.
However, you must get user consent before collecting his anonymized data and passing it to the data collectors. 50k+ DAU is enough to get the decent revenue PLUS data monetization SDK won’t harm your existing SDKs and monetization model that you’ve applied before.
On the off chance that you truly need to indicate promotions then you a basically “bolt” the application/amusement if there is no Internet association and demonstrate a discourse that information association is required to open this application
If we are talking about android apps, now there are a lot of ads able to be downloaded on cashe of user’s device.
In this way you can prmoto your products when smartphone owner isn’t online.
Some VPN services, for example, can download ads in their data storage. Like Hotspot Shield:
And, of course, you can recieve the e-mail adress of user and do letters promotion. I can’t say that this method is very effective, but it also gives some important results.