Android AAR file protect from reflection

I have big problem with AAR files. I want make an AAR file and give it to some other businesses to have payment solutions with our business (like PayPal AAR file) and i don't want they can reflect our class members and they can't have method call (of course in a reflect way) from their apps. Is there any way to protect my code from reflection. Of course java has security manager but in android we just set null to security manager.