The $300,000 gift should be reported on Form 709 since it exceeds the annual exclusion of $18,000 for the 2024 tax year (note that you do not need to report or file).
See https://www.irs.gov/forms-pubs/about-form-709
However, no gift tax will be due unless the transferor has exceeded the lifetime exclusion of $13.61 million.
See https://www.irs.gov/businesses/small-businesses-self-employed/whats-new-estate-and-gift-tax
