More detail
There are really two costs to non-compliance: direct penalties for not issuing proper invoices, and the indirect hit that expenses lacking eTIMS support may be disallowed, raising your taxable profit.
Rather than quote a figure that may be out of date, the responsible guidance is to treat non-compliance as a real and avoidable financial risk, and to confirm the live penalty position with KRA or your accountant.
Related questions
How much is the eTIMS penalty?
Can non-eTIMS purchases be disallowed?
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