Well, there are several questions, come on:
How to create a payment system via ticket or card, there is some
framework or company that offers the service?
Via ticket, it's easy, talk to your manager so he can give you some numbers that you'll use. Some banks provide the example code to create the ticket, I did once with the Federal Savings Bank. You can also search for an external solution, I came to see but did not use: link . The tickets usually have a deadline to confirm receipt after paid and do not expect to be as short as that of large stores, when I did for example took 2 to 5 days depending on a lot of things.
Card is more complicated, you talk to the card operator you are going to receive, it usually involves a transaction, you send a data packet, the operator's server responds, you send another confirming or with some other data, and finally , receives the finalization.
If there is an attachment to the site?
In the case of tickets, record the identification of the ticket in the information of open payments, in the case of card, usually payment is in the act, but there may be a different treatment that I do not know, will depend on the operator. You can use "our number" and "document number" to identify the ticket. The "our number" is unusual for identifying each ticket, but in my case I had to use it.
How to post tickets?
It sends the values to the application that generates them and it generates, without any complications, but there is also no registration, you should register in your code.
, there is some framework to aid in the creation of pdf,
should these have a fiscal validation?
Yes, example in the answer to the first question but not in PDF, it is not necessary. There are also paid solutions, super easy to find on Google, looking for "online ticket" appear various solutions. You do not need tax validation, but a word from your manager is recommended. For example, for what I developed for use in the box, we generated three tickets together with the manager and checked if everything was valid.