We generalize the approach defined in D. Bolignano's "An Approach to the Formal Verification of Cryptographic Protocols" so as to be able to formally verify electronic payment protocols. The original approach is based on the use of general purpose formal methods. It is complementary with modal logic based-approaches as it allows for a description of protocols, hypotheses and authentication properties at a finer level of precision and with more freedom. The proposed generalization mainly requires being able to express and verify payment properties. Such properties are indeed much more elaborate than authentication ones, and require a significant generalization in the way properties are expressed. The modelling of the protocol and of the potential knowledge held by intruders is on the other hand left unchanged. The approach is currently being applied to the C-SET and SET protocols, and has already lead to significant results.