Every tax invoice we raise splits one of two ways, and the split is decided before a rupee is charged.
One field, stated explicitly
Place of supply is its own field on the customer record. It is never parsed out of a free-text address and never inferred from the GSTIN, because both are guesses dressed up as data — an address line can say anything, and a GSTIN's state code tells you where a business registered, not where a supply was made.
What it decides
Compared against our own registered state, it settles whether the invoice carries CGST plus SGST or IGST. The rate itself comes from the plan being sold, so a mixed order is taxed line by line at each line's own rate rather than at whichever rate came first.
Why an activation refuses without it
An invoice cannot be raised without a place of supply, so the activation refuses at the point of sale rather than after the money has been recorded. It is a worse experience for thirty seconds and a much better one than a corrected invoice a month later.
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