Chiffre d’affaires for the month I moved to France - payment dates

Happy New Year Valerie!  And I hope you had a lovely Christmas.

This month, I have to do my first French chiffre d’affaires for September, October, November and December 2020.  I’m quite confused about what I need to do regarding the dates and I would really appreciate some clarity on it.

Before I moved to France

Before I moved to France, I was a citizen and resident of the UK.  I had been doing the same activity as my French activity (teaching English for international agencies) in the UK for a short time.  I had set up as a ‘sole trader’ in the UK before I moved to France, but I earned less than £1000 in the UK before I moved to France.  My UK ‘sole trader’ account is still open as I may have to do a self-assessment in the UK later this year (although this is uncertain due to the small amount earned).

September

On the 12th September 2020, I moved to France and my micro-entrepreneur status was set up to start from that day.  I had worked physically in the UK from the 1st-11th September.  There is some work that I did physically in the UK between the 1st-11th September, for which I didn’t receive payment until I was physically in France and set up as a micro-entreprise in France.

On my French chiffre d’affaires for September:

1. Is it possible to declare the work that I did when I was physically present in the UK from 1st-11th September, but that I received payment for when I was physically present in France and had my micro-entrepreneur status set up?  For Brexit reasons, it would be beneficial if I could declare this income on the French chiffre d’affaires, just wondering if that’s ok?  To be specific, there was:
a) One class via one agency that I taught on the 11th September, and received payment for on the 14th September
b) Another agency paid me via one lump sum on the 8th October, for work done in the month of September (some of it was done from 1st-11th September when I was physically present in the UK, some of it was done from 12th-30th September when I was physically present and set up as a micro-entrepreneur in France).  Can I declare that whole lump sum amount on my October chiffe d’affaires, or do I have to subtract the amount for the work that I did from the 1st-11th September, before I moved to France and had my ME status set up?

2. Will I need to declare the payments I received from the 1st-11th September (when I was physically in the UK and before my micro-entrepreneur status was set up in France) on my French chiffre d’affaires for September?  I’m guessing this is a ‘no’ but I just want to be sure because I’m aware of the concept of dual tax residency etc.

3. I would also just like to double-check that it is possible to declare income earned from 12th September when I was physically in France on my French chiffre d’affaires.  I’m pretty sure this is an obvious ‘yes’ but wanted to check I can declare income in France when I also have a ‘sole trader’ account open in the UK.

Thanks