Have you already applied for an EFIN on the IRS website?  If so, what does it show under EFIN Status?

It may take a while for the EFIN letter to come through but you can print out the EFIN Application Summary from the IRS website for submission to Intuit to register your EFIN.

You will not be able to efile until your EFIN document has been reviewed and accepted by Intuit.  The process is said to take 2 business days but I have seen them approving it within the same business day.

https://accountants.intuit.com/support/en-us/help-article/account-management/register-efin-proconnec...

https://accountants.intuit.com/support/en-us/help-article/electronic-filing-identification-number/su...