Is my work and spending my salary in a pharmacy that exchanges insurance prescriptions for other products unlawful (haram) in Sharia?

If the insurance allows for the replacement of medication, then there is no harm in it. However, if it does not allow it, then it is not permissible to replace it because it constitutes fraud, and it is not permissible to assist the pharmacist in this act. As for the salary, it is not rendered unlawful merely by this assistance.