Google Wallet reads your device info, including the build.prop file, to verify your phone is supported. If this file doesn't contain the proper information, the app disables tap and pay. Even performing the mod to change the 4G symbol breaks GW with a fully stock ROM.
Your only bet is to either return to stock or download Xposed (if it works for CM) and install the Wallet Patch. However, I don't know if the patch helps with the recently released GW update.
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