I have submitted my manuscript to a journal. After several weeks the editor sent me the comments of two reviewers. The editor said that "the authors should provide proof that the paper has been proofread by a native English speaker".
So how can I provide the proof? Should I send the proofreading certificate which I recieved after using the service from a proofreading company?
And if I only ask a native speaker for proofreading without any certificates, how should i provide the proof?