Build an ISO 20022 pacs.002.001.10 (FI-to-FI Payment Status Report) in the browser. This is the message that carries the ACSP / ACSC / ACWP / RJCT / PDNG status codes the Ohmyfin tracker explains. Validates the original message identifiers, the transaction status code list and the reporting party BICs.
OrgnlMsgId is the MsgId of the original message you are reporting on (e.g. the pacs.008 you received). OrgnlMsgNmId is the message-definition identifier — e.g. "pacs.008.001.08".
Is the UETR mandatory?
Not on pacs.002 itself, but if the original message carried a UETR you must echo it as OrgnlUETR so the tracker can correlate the status to the payment.
Can I send a reject reason?
Yes — supply statusReason (e.g. AC01 for invalid account, AM05 for duplication). The form emits StsRsnInf/Rsn/Cd with your code.