You are lucky, it seems like a case where hybrid apps are interesting. There seems to exist an inflexion point where hybrid frameworks become an hindrance and it is more productive to just go with native.

You should start by having a look at either Xamarin, Flutter or React Native.

They are rather good multi platforms solutions.

To me, there are two orthogonal ideas in the question. One is solving an organization's problem. The other is an individual learning app development. The members of the organization are better served by one approach, the individual will learn more from another approach.

To me, the amount and type of work that is likely to be required in order to change a significant organizational process might be better put to simply learning to build apps for something else. The skill set to change an organizational process is probably orthogonal to technical skill as well. I mean the premise of the app is along the lines of "everyone is doing it wrong" and that's a hard sell. The sale requires building allies among the people in a position to institute the change and to sell it to the hundreds of thousands of members as a benefit...and there are probably people like me among the membership who would rather have a card than something on their cell phone and maybe a few who run Windows on their phone.

Good luck.

The thing is unions in France are really short-handed and do not have a lot of money. Hiring a "top notch" consulting firm to develop the app is not financially doable.

I'm not saying, "everyone is doing it wrong". I'm saying "everyone is doing it like it was done in the 1950", because it's true.

Now the top brass wants to modernize everything. I just made for them a brand new website, they want a Facebook/Twitter presence and everyone agree that the old "member card" is a problem.

My thinking is that for these kind of people, I'd have a better chance of convincing them by showing something already working (I'm totally ready to get a "no" even if I worked on the app 100 hours, I would have learned new skills in the process anyway).

Of course, at the beginning we would offer people the choice between the paper card and the e-card.

I'd put it another way...if digital cards in the form of a mobile app are viable, then why have cards at all? Just verify paid dues against a database and authenticate using an existing form of id such as a passport or other government issued document. I mean even with a mobile app, sound practice would be to authenticate identity using a third party service rather than something created in house.

There's the possibility of a hybrid approach where a physical card is permanent and the cardholder's payment status is verified against a database. And perhaps a delinquent status can be fixed by swiping a credit card using Stripe or a similar service...that might even increase membership renewals by reducing friction.

I'd put it this way, building an app using developers without experience is kind of 'doing it like it was done in 2009.' In the interim people's expectations have become higher and building a quality multi-platform app requires more sophistication. Not to mention maintaining one has become more complex as the app store requirements change and hardware diversifies, e.g. the latest iOS requires 64bit compilation.

To me, the business problem is not the lack of an app. It is the process of maintaining the union's membership roll. An app doesn't really solve that.