Both FIRA and FIRC help to prove that there is inwards remittance to India
Though they differ depending on who issues it and for what purposes, both FIRA and FIRC are sufficient in proving that the transaction was made inwards into an Indian bank account for an exporter.
Foreign Inward Remittance Certificates are only issued for Foreign Direct Investments (FDI) or Foreign Institutional Investments (FII) for Physical Foreign Inward Remittance Certificates, and transfers for the exports of goods, software, and other services for Electronic FIRCs (e-FIRC).
All other use cases will be issued an FIRA.