Applying for an A1 certificate to work abroad as a sole trader (CA3837 form)

Hello, I am hoping to undertake some short-term self-employed work in Europe this summer and am needing to apply for an A1 certificate (using the CA3837 form). I understand that if you have been registered as a sole trader for less than 2 months prior to applying that additional evidence of self-employment is required to support the A1 application. Would anyone know or have experience with what specific evidence is needed for this? I am still full-time employed but have been doing a small amount of self-employed work on the side. Would generating a few small invoices from self-employed work over a couple of months be sufficient, or would I be expected to have self-employment as my only source of income for this 2 month period? Any help would be much appreciated.

Hi mewtight3 Wright,
If you haven’t already registered your self employment with National Insurance you’ll need to do this first. 
If you need to register as self employed you can do so here:
Register for Self Assessment if you’re self-employed
Please note, you need to keep a note of the start and end dates your self employment for your own records.
It’s not the responsibility of HMRC to keep these details.
You’ll then be able to complete the CA3837 form you’ll need the start date of your self employment that we hold on record through your registration. 
You can find the application and more information here:
Apply for a certificate to confirm you will pay UK National Insurance while self-employed abroad temporarily (CA3837)
Thank you.