What should I check if the invoice SAC or HSN and the purpose code seem inconsistent?

Check the description of what you sold first. The invoice classification and the remittance purpose code serve different reporting roles, so do not try to make their numbers match. Each needs to describe the actual supply correctly in its own system.

Ask your accountant to confirm the SAC or HSN used on the invoice and ask Skydo support or your bank about the remittance purpose code. Share the same invoice description and supporting agreement with both so the explanation is consistent. If either field is wrong, follow the correction process for that record. Do not change a code simply because another invoice used it or because it appears to remove a processing query.