Ok ... let's start with the third payment ... it will be released based on the filing of the 2020 return if you are eligible.
Next the missing second check ... if you got a letter saying they sent it then you will NOT get it on the 2020 return as a credit. YOU will need to ask for a trace on the missing money to be initiated .... read the third + :
https://www.irs.gov/coronavirus/second-eip-faqs
