how can we implement payment gateway in LTI extentions
I think you would implement it the same way you would in any other application. The LTI launch will give you the benefit of knowing the user's identity, but you will still need to implement the payment functionality - securely taking and processing a credit card.
Could you provide some more details about what you are trying to do? Is this a third party payment gateway you are trying to adapt? What type of information do you want to go from Canvas to this application? What do you want to go back to Canvas (if anything)?
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