F.A.Q - Can I import data directly into a custom opportunity form?

You cannot import directly into an Opp form BUT you can do an Opportunity FUM into one. Run your import then run a FUM into the Opportunity form. Best practice is to download the imported data so that you can get the recdno but if your data has a unique field in it where you are sure the data is not duplicated in the db then you don’t need to download to get the recdno, you can just use the original imported data.