continued error when trying to collaborate on numbers

Have you visited Apple's support documents?

Intro to collaboration in Numbers - Apple Support

Invite others to collaborate in Numbers on iPhone - Apple Support

SG

Umm.. not much to go on there...

What kind of error? What error message (if any) do you get?

Are the phones using the same Apple Account? or different ones?

Does it happen with every spreadsheet? or a specific one?