Praise be to Allah.
Firstly: Dealing with Visa and credit cards when buying and selling
It is permissible to use credit cards and Visa cards for buying and selling if that is free of any infractions of Islamic teachings, which have been explained previously in the answers to questions no. 97846 and 97530 .
There is nothing wrong with designing websites with permissible aims and goals, even if they offer the service of buying online.
We should point out here that it is permissible for the seller – whether online or otherwise – to sell his product to someone who uses a Visa card in all cases, without inquiring into the matter and trying to find out how the purchaser uses it, and whether he has credit on his card or not, or whether he is subject to a penalty in the event of late payment or not, because the seller is not required to do that, and he is not obliged to ask the purchaser about the source of his wealth. Rather all he has to do is avoid dealing with anything that is haraam, such as selling gold to someone who wants to buy it with a credit card. Moreover, some purchasers may use a haraam credit card, but in a way that is free of committing any infractions, as is well known in the case of what is called loading the card, in which a person loads the card with the value of the purchases, then he buys whatever he wants, and thus avoids infractions.
It is not permissible for designers and programmers to help in anything that is haraam, such as designing anything that promotes gambling, drinking of alcohol, prostitution, and other haraam actions.
Secondly: it is not permissible to contribute to programming for anything that has to do with the sale of haraam things
It is permissible for you to work in this company on condition that you do not help in anything that is haraam, as noted above. So you should not contribute to programming for anything that has to do with selling haraam things, advertising them or promoting riba-based loans. However, you may continue to work until the nature of the upcoming work becomes clear to you. If you can avoid doing anything that involves any infractions of Islamic teachings, then carry on working, but if you can find work that is free of dubious matters and is “clean” in all aspects, then that is undoubtedly better.
Thirdly: There is nothing wrong with doing what you have been asked to do of making a library of codes for the company, which can be used later on in any new website, even if we assume that it will be used for websites that deal in e-commerce, or that deal with banks and hotels. Simply making a website for buying and selling and recording the user’s credit card number is not haraam.
We praise Allah, may He be exalted, for giving you the eagerness to seek what is halaal and keep away from what is haraam, and making you concerned about that. We ask Allah, may He be exalted, to continue to help and guide you.
And Allah knows best.