If anyone sent me an email like that, I'd cancel everything I'd done with them and make absolutely certain they had no valid card info.
You store passwords in a recoverable manner - i.e. text - and you are complaining about Gmail stopping less secure apps working?
Never store passwords in clear text - it is a major security risk. There is some information on how to do it here:
Password Storage: How to do it.[
^]
And remember: if you have any European Union users then GDPR applies and that means you need to handle passwords as sensitive data and store them in a safe and secure manner. Text is neither of those and the fines can be .... um ... outstanding. In December 2018 a German company received a relatively low fine of €20,000 for just that.