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What St. Thomas Aquinas wrote in Summa Theologica II-II q. 189 a. 9 co. regarding inducing others into the religious life can be applied, mutatis mutandis, to making converts:
[To] persuade another simoniacally to enter religion, by giving him presents […] is forbidden […]. But this does not apply to the case where one provides a poor person with necessaries by educating him in the world for the religious life; or when without any compact one gives a person little presents for the sake of good fellowship.
Thus, if the financial incentives have no contracts attached to them, they are not simony but free gifts.