I am a little confused. Are you electing on Form 2553 for the client to become an S Corp for the tax year 2022 and filing an extension for the client as a sole proprietor for the 2021 tax year? Or are you filing a Form 2553 for a 2021 return and also filing an extension for that same return as an 1120-S?  Additionally, you could fax the 2553.  The fax numbers to use are in the instructions for the form.

Another former All Star