I have some news/ press coverage on the partnership signing ceremony - will show that on the website for more credibility.
"the code is clean and does not have any back doors." -> we are not able to show our code source, we did pass bug hunt and tests of some cyber sec organization.
It is not a matter of showing the code as much as you can notify the customer that it is safe. If it is impossible to show a portion of the code, it is better to ask trusted companies or even individuals to help you.
Do not forget to publish the correct news, the developed team and others, the free period does not mean anything for an anonymous application.