Http post on a webserver error

Hello everybody,
Recently I have the problem that I can not make any posts in my Ionic app that have my local Dev server as my target. But posts to the live server are possible. I suspect that it has to do with the SSL certificate on the dev server, since this is always displayed as invalid. And posts only work on the live server which has a valid certificate. The problem occurs only a few weeks ago. Does anyone have an advice for me how I should configure something?