If they didn't tell you in person it should be in the letter, but did anyone specify what it was that caused you to be declined?
Is it past credit issues, or is it criminal background?
If it's credit, do you currently have high levels of dept and/or are you currently under collections? Have you previously declared bankruptcy?
If it's criminal, do you currently have legal proceedings in process against you? If not, how many charges have you previously been convicted of, and as previously mentioned, have you obtained pardons for them?
If you were declined due to ongoing issues, then you obviously can't be cleared ERC until proceedings are done.
If it's because of past records, then you need to take the steps to clear it before you would be.
Do you have questionable contacts, ie, an uncle in the HA? Who were your references, and would they be considered upstanding citizens? Would they have had good things to say about you? Do you actively associate with people who have a criminal background or are involved in questionable activities
Once you get the letter, it'll state "based on the information currently available. If anything has changed, contact..." or something to that effect. At which point this is where you would provide documentation that ex: you've paid off your debt, been pardoned, completed legal conditions, etc.