Accountants letter of confirmation.

I am applying for my wife's U. K. "FLR" immagration visa.
U. K. Immigration have requested a accountant’s "letter /certificate of confirmation"

I am a Sole trader/self employed 9k per annum, approx .

Every year I undertake my own accounts, each month I list my "incomings and outgoings" . of which there isn't much to add to my excel spreadsheet . I then add that to my own annual tax returns. I do not sell products or merchandise. I offer my service as a "Sound recordist" and invoice accordingly. As I am a Sole trader, I am not required to submit "Audited Accounts" each year.I submit "Unaudited Accounts"
But I now need a accountant’s Certificate of confirmation.
Thank you so much.

Important accountants requirement
Please read below.

Only an accountant who is a member of one of the following can provide me with this document:

a UK Recognised Supervisory Body (as defined in the Companies Act 2006); or
the Institute of Financial Accountants;
The Association of Authorised Public Accountants;
The Chartered Institute of Public Finance and Accountancy;
The Chartered Institute of Management Accountants;
the Association of International Accountants; and
The Association of Accounting Technicians."