How to prove extension was filed for Form 1065

[gdh-cg]

Received a huge bill for late filing of form 1065 even though an extension was filed.  How can i prove that the extension was filed in a timely manner?  Did not send certified or return receipt.

[Anonymous_]

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@gdh-cg wrote:
....Did not send certified or return receipt.

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Not good, but you can send an explanation letter to the IRS along with a copy of the extension you filed (if you retained a copy, hopefully).

See https://www.irs.gov/instructions/i1065#en_US_2022_publink11392vd0e1211

[Opus 17]

Hopefully, you filed form 7004, to request an extension on a business return?https://www.irs.gov/forms-pubs/about-form-7004

It is not the same as requesting an extension on a personal return.