One trick might be to just put a 10% higher price within the app, and lower off app. Consumers will think it's a mistake and spread the word. You can also send them an email telling them that they get a discount if they subscribe now.
On the other hand, some people prefer to pay within app. I don't trust many subscription services to be responsible with my credit card information, but Apple/Google have proven to have consumer protection. So you should probably do both.