[Closed] Excel online - form controls error message

I'm getting the following error message on an excel form which I've uploaded to a SharePoint based website. The message appears where form buttons controls should be:

"Excel for the web does not support running or interacting with form controls. To use form controls open this file with the desktop app."

I then get this message when trying desktop app instead:
"Excel cannot open file because the file format or extension is not valid. Verify that the file has not been corrupted and that the file extension matches the format of the file."

Any suggestions re possible solutions?

Thanks